While you all brought up some very good points, I have to agree with Fateless and stand by my original point. The class feature specifies "As if you were there" and the wording essentially denotes that all the implications of you being there yourself are plausible as well. If the feature intended for you to cast a spell through the mind so as to avoid counterspell, I believe it would have been worded more like Find Familiar, which states that your familiar delivers the spell as if it had cast the spell, thus the wording should be, on the class feature, something like "You cast the spell and it originates from your manifest mind's space" or something of that nature. Instead the class feature goes out of its way to be very specific and state that the spell is indeed cast as if you yourself were present there casting it. If we interpret it like that then that spell is cast as if there is indeed a creature within view 60 feet away. Otherwise the wording of the class feature doesn't make a lot of sense when there is already a precedent for this specific wording in other spells. It could've said "Casted from your manifested mind's space" as well, but instead it specifies that it is being cast as if you are in that space yourself.
Hell yeah! I love this feature of the order of scribes wizard. I'm playing it in an upcoming campaign, and as you have already mentioned, point-blank fireball using the manifest mind feature is AWESOME! And that misty step interaction! The "mind" can travel 300 vertically as well, helping you get up or down terrain with ease. I don't think the mind can be affected by spells like invisibility, as it is intangible, but I could be wrong. There might be some great illusion trickery by maintaining the illusion of a creature over top the space of your spectral mind! Some other ideas:
Counterspell requires them to see you casting the spell, so you can safely hide 300ft away while your spectral mind casts spells against enemy magic users.
An elemental conjured by "conjure elemental" lasts for 1 hour and will turn hostile instead of vanishing when you lose concentration. Conjure that bad boy 390ft away from you while hiding and immediately break your concentration. It will attack the enemies around it, and you can concentrate on something more useful... or summon another!
Convince an uncivilized group of creatures that the spectral mind (looking like a wizard of old) is their god, by performing magic and daring them to try to harm it. When they are sufficiently worshipping you, emerge from hiding and enjoy the benefits of godhood!
Use it as an extremely effective distraction-generator. Rogue trying to steal somthing? Guard see through your disguise self? BOOM! Explosion 300ft away.
Make use of awesome melee and cone spells without putting yourself in harms way!
guard three entrances/exits at once using yourself, your spectral mind, and your familiar!
put on a great 5-person show with mirror image, major image, and spectral mind!
look extremely wizardly by "reading" a ghostly tome or wall of text floating in front of you while sitting or travelling.
Sneakily get past an opponent blocking a doorway by summoning the spectral mind in their space, moving it behind them, and misty stepping past them.
Look INSIDE creatures, as you can see with your spectral mind, it sheds dim light, and it can "pass through creatures". I would give extra information to a wizard who did this on a medicine check, if they were well-studied in medicine.
Teleport your unlucky party members out of the belly of the monster that swallowed them, like a purple worm or froghemoth!
Pick up the new eldritch invocation feat to get "Gaze of two minds." Normally, you are blind to your own surroundings while using this, but not when you have spectral mind also giving you sensory input! Maintain a connection with your forward scout while sticking with the main party, giving instant relaying of critical information.
If you, for some reason, have 5 levels in cleric or druid, you can cast Meld into Stone and be super safe for 8 hours, casting spells as normal within the 300ft "leash" of your spectral mind.
Instead of hiding while your spectral mind is front and center in combat, you can be alongside your teammates for buffs/safety while your spectral mind hangs back or scouts for an escape route/ advantageous position.
If, for some ungodly reason, the weather outside is too terrible to even step foot into, you can stay warm and snug inside while your spectral mind goes outside to cast control weather.
Cast "knockback/pull" spells and cantrips from a different angle! Thorn whip a foe off a narrow mountain pass, push the entire line of charging enemies 15 ft to the right or left using gust of wind!
Give the local crime lord a gift of a chest, heavy with coin and also your spectral mind! Hopefully they open the box within 300ft of you, so you can "pop out" using misty step, or the spell "silence" to avoid people outside the room hearing the racket of you making short work of your foes.
make a kid's day by giving them the spectral book, and telling them to shout out whatever spell they'd like to cast, making the magic originate from where they are.
Frame a famous witch or wizard by summoning your spectral friend inside them and casting lightning bolts into the crowd while they give a speech.
Scout inhospitable environments: room full of poisonous gas, vat of acid, icy water, any sort of death-trap room that would kill a familiar scout instantly.
Give your dm a way to incorporate famous wizards from their setting into the game!
Create an antimagic field right on top of an enemy spellcaster/benefiting from magical effects. Your spectral mind will be temporarily suppressed, but the field should remain! Get a beefy teammate to move in and immobilize the enemy in the field.
This part specifically "Counterspell requires them to see you casting the spell, so you can safely hide 300ft away while your spectral mind casts spells against enemy magic users."
This is not entirely true actually. The ability to cast a spell through the manifest mind specifically says "Whenever you cast a wizard spell on your turn, you can cast it as if you were in the spectral mind’s space, instead of your own, using its senses. You can do so a number of times per day equal to your proficiency bonus, and you regain all expended uses when you finish a long rest." The key bit here is "you can cast it as if you were in the spectral mind’s space" So if you are casting a spell as if you were in that space then counterspell can target you, a creature, casting a spell within range since the spell you cast through it is cast as if you were there.
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While you all brought up some very good points, I have to agree with Fateless and stand by my original point. The class feature specifies "As if you were there" and the wording essentially denotes that all the implications of you being there yourself are plausible as well. If the feature intended for you to cast a spell through the mind so as to avoid counterspell, I believe it would have been worded more like Find Familiar, which states that your familiar delivers the spell as if it had cast the spell, thus the wording should be, on the class feature, something like "You cast the spell and it originates from your manifest mind's space" or something of that nature. Instead the class feature goes out of its way to be very specific and state that the spell is indeed cast as if you yourself were present there casting it. If we interpret it like that then that spell is cast as if there is indeed a creature within view 60 feet away. Otherwise the wording of the class feature doesn't make a lot of sense when there is already a precedent for this specific wording in other spells. It could've said "Casted from your manifested mind's space" as well, but instead it specifies that it is being cast as if you are in that space yourself.
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This part specifically
"Counterspell requires them to see you casting the spell, so you can safely hide 300ft away while your spectral mind casts spells against enemy magic users."
This is not entirely true actually. The ability to cast a spell through the manifest mind specifically says "Whenever you cast a wizard spell on your turn, you can cast it as if you were in the spectral mind’s space, instead of your own, using its senses. You can do so a number of times per day equal to your proficiency bonus, and you regain all expended uses when you finish a long rest." The key bit here is "you can cast it as if you were in the spectral mind’s space" So if you are casting a spell as if you were in that space then counterspell can target you, a creature, casting a spell within range since the spell you cast through it is cast as if you were there.