I've seen where people have done modest painting that looked good. If I were going to change the interior color I would go for a two color theme. You can go to salvage yards and find small things like vents, speaker covers, consoles, dash pieces etc.... or you could redo the whole interior, but that would be a pain in the ass....

I've actually used Krylon Fusion on wood plastic and metal, and I can honestly say that it sprays on very well. It sticks good and has a beautiful overall look..... on smooth surfaces anyway. The problem with interior pieces is that they are usually not smooth at all. And they have some really crazy curves that you'd have to hit at just the right angle. I would strongly recommend against painting interior pieces. It usually never works out very well.