Absolutely clean it, but I would only replace the parts that absolutely need to be like the cables and bearing grease. However, since the back wheel is aluminum finding an aluminum front (shouldn't be difficult or expensive) would definitely increase the appeal of the bike a lot. Put tires on it of course. Then sell it as-is. I would not bother with decals, it wouldn't be worth the money.

I would say in excellent ready-to-ride shape a bike like this would only be worth $100-125 with all the original parts anyway. It's too low end to stick a bunch of money into.