The only downside I've heard people really talk about is that it destroys the value of a vintage bike, but I doubt this is one of those. There is cost depending on how you want to do it. So, no downside if you want to freshen things up a bit. It might strike some as unnecessary as it is for largely cosmetic reasons...however, people put all sorts of effort into such things they enjoy (cars, houses, yards, clothes, etc.), if painting it helps you enjoy it more, do it. Personally, I have an '86 Trek with alright paint I've considered re-painting. Yeah, it'd take down some of the resale value (from a few hundred dollars!) and some people, philosophically, would be opposed to it. but I've put so much time into customizing it and making it my ride...the frame is pretty much the only original piece. I'd just like it to have a nice coat of paint.