Yeh experimenting would be a good idea if possible....I did it to my OEM lights (bought a spare set for like $80 in case I didnt like the look of it). I went a little darker whilst still being clearly visable....the only issue is since I only put 2 very light coats on....the spray came out a bit funky and looks blotty if you are standing really close (could have just been the way I applied it I.e. can was cold and maybe it was my noob overspray). I might try and take a pic next time if I remember....but upclose its not the best.
I dont have many pics of the car from the rear....but you can kind of see if in this pic:
Or this one shows what its like in the sun (right tail light) and in the shade (left tail light):
Also not 100% how the plastidip and nite shade will interact with one another.....its a smart idea, but maybe the nite shades wont apply properly? Again, if you got that spare perspex or whatever, then give that a try first and see if it works/can be peeled off?
And good plan on the brembos....wish I could afford them.....keep your eyes out on gumtree bargains, etc....pretty sure I've seen a couple complete sets of 4 pot rears around $1200ish....plus was spewing I couldn't afford this other bargain I saw which was 6 pot front setup for $1200 (eastern states though) - needless to say that advert sold that same day lol