I have a drow rogue/ranger who currently has a 28 PP and 20 PI. I have an odd wisdom score and plan to take a half-feat next level. I'm leaning towards making my passive perception and investigation crazy high but do I really need it that high? In two levels my PP will be 31 anyways just from the +1 wisdom and leveling. Does anyone think its worth making it 36 and getting read lips? 

Other options are probably fey touched for misty step and maybe hex (bless wouldn't be bad either) or telepathic as I think it would be super useful scouting to talk to teammates but also role play of telepathically talking to strangers during encounters etc. 

I already have drow high magic so I'm at-will detecting magic, I have 150' darkvision, and 10' blindsight. I'm looking at Devils Sight as my last feat, or I could take it now and not raise my wisdom until the end. 

So back to the question. Is going crazy with PP and PI and reading lips worth it?

Well it truly really depends on the campaign setting you find yourself in. In a more high crime and intrigue campaign where investigating and perceiving are more important than beating your enemies to death with a stick, then absolutely. If you find yourself fighting people more often, then there is a lot more to consider.

NPC's and humanoids, if your DM so chooses, can make your NPC's have classes. And so then it's important to understand that anything you can do, they can do. So if you consider how ridiculous stealth bonuses can get, then perhaps having a ridiculous PP is a normal thing to have, as an NPC can absolutely have classes in rogue and ranger and things of the sort. Even without this, the relatively low level spell "Pass without Trace" adds a whopping 10 to stealth checks of the caster and it's allies, which reduces their necessary roll of your PP by 10 plus whatever base bonus they originally had. So with the proper spells (Pass without Trace, Enhance Ability, so on), even NPCs can hide from a 31 PP. In addition, there is always a nat 20 but you can't really do anything about that.

I hope this helps!

a current reoccurring theme in our campaign for enemies are Devils, Dragons, and Undead. We are 15th level so we are talking very powerful version of each. Many times far more powerful than we can fight, and we need to work-around for many levels until we can confront them.  

I ended up with a level of fighter just to get blind-fighting as a second fighting style because of devils uses of magical darkness and my having an eversmoking bottle which can neutralize a lot of problems... So Devils Sight will be highly useful for me given our projected enemies (we are at the point in our campaign that we know the general direction and what type of major enemies we will face based on prior campaign decisions.)

So Devils Sight or more wisdom and perception...

Misty step also would have already been very helpful as we've had a few versions of walls put up to split the party, and its not uncommon I'm one of the ones isolated. 

I love the idea of being a demi-god at perception but so many competing options...

as far as damage output, its not a concern for me at all. I have no desire to increase my combat ability, its great and cant be improved much even if I wanted. I have archery fighting style, elven accuracy, and sharpshooter. Three attacks first round of combat and sneak attack..

I'm doing more than fine in the combat arena. I really want to be better at other important things as I am the reconnaissance specialist for the party. I wear an elven cloak, fly a broom, and have expertise stealth. So stealth is also covered as well as it could be. 

Perceiving even more all the time (observant), seeing in almost all conditions (devils sight) not getting stuck and being able to get unstuck (misty step) , higher saves (bless), screwing the enemies saves (hex), reading lips (very situational and probably not very important, but very cool)

Those seem my best options overall. Much of it doesnt matter if you dont notice the important things etc which is what makes me lean towards observant or devils sight

These types of enemies tend to have magic that surpasses high Passive Perception scores, such as invisibility, darkness, blindness, eyebite, and so on. These types of enemies might have Devil's Sight, which makes it possible for them to view through magical darkness, which is superior to standard darkvision as Im sure you know.

If the choice is between more Passive Perception, more combat, and more utility, with the information provided, I suppose that utility is the best outcome, as 31 Passive Perception is already astounding, not many creatures will defeat that without a critical success or straight up invisibility. Having more utility can help out of combat, but also within combat if you choose the right utility. An example of this is a simple fog cloud. Blinding creatures within is powerful, and Devil's sight cant help against that. But Fog Cloud can also help out of combat by causing a distraction or masking certain actions that your tabaxi is taking.

Most importantly, whatever choice fits the roleplay vibe youre trying to go for. So if your character is the demi god of passive perception (PP Prince if you will), then perhaps, for flavor and roleplay, you select observant.