Darkvision

Why wasn't this given an upcast for more targets? You seem to have added upcast to most other spells that could logically have one.

Because 3/4ths of the party have natural darkvision

How in the world is this not divination or enchantment. In what world is this transmutation!?

Darkvision is common enough for both PC's & NPC's that darkness rarely has a mechanical effect in combat, unless the DM goes out if their way to make it one. Someone with a greater range to their darkvision could potentially abuse that against a creature with shorter range tho, and 150 feet makes 90% of creatures fair game for that strategy if you're a long ranged character.

Would this combine with Shadow Monk darkvision? Increasing it to 210ft?

Upcasting it isn't very different from just casting it at first level repeatedly. If you're casting this in combat you're doing something wrong.