spray painting a yoyo

would this work?

Yes, a lot of people do it. Some people use automotive paint, and some use a clear coat on it as well.
Surface prep is the key to success.

Beat me to it, lol. Prep is most important part when working with a rattle can, not that I have ever sprayed a yo yo but just about everything else. A clear coat on top would smooth it out and gloss it up a bit as well. Auto paint would probably work well, or krylon makes a plastic paint that would probably spray on pretty well.

Hmmm. Would the High Temp. BBQ Grill type paint have a good enough surface to grind on? Make one Stealthy and grindable?

That might work it gives a flat black finish that may slow you down a bit on grinds. I used a satin black when I sprayed a buddy of mines wheels for his truck with a top coat of clear that gave it a sort of slick feeling that may work pretty well. It was rustoleum with a spray trigger on it I think that makes application pretty simple too making your coats more even.