Paint will not hurt heat dissapation. Some think that black paint acutally helps by drawing some of the heat to the dark layer of paint, helping you to better dissipate heat (i.e., car radiators painted black). However, paint is a PIA to keep looking good because it tends to get scraped and scratched.
As far as value, not really a collectible bike that I'm aware of. The value is what it's worth to you or the potential buyer. It will be worth more in perfect shape. Restoring mid-80s bikes is usually not a profitable venture, if you're looking to make a profit. However, you might always find someone with a lot of money that grew up riding one and wants to relive a part of his childhood and is willing to part with a chunk of money.