In my opinion, keep an original car original. My 68 ‘02 is mostly original to my knowledge and on the visible things that are wrong; I do my best to research and make it right. (Mike Self can make a list, I’m sure)
There are some things that you can do that future owners will appreciate as long as the appearance is kept stock and clean. These things can also increase your value. Carbs, Shocks, Wheels (period are best, nothing fancy) 320i rear drums, better seatbelts for example are things that enhance your safety and drivability of the car, but won’t bother a future owner. (Save your parts!) Please resist the temptation to add a CD/DVD player, amps and subs in the trunk….the best music is found under the hood, or out the rear pipe—don’t ruin it.
Enjoy!
Ben