Thanks guys, I really appreciate all your comments!!! For fingernail polish, the best thing to use to thin it is cheap lacquer, has always worked well for me. Make sure to use a good primer to seal your plastic, I have heard of some people using future floor wax on the bare plastic first and then primer and so on....
Nail polish is very thick so I suggest that, before you even try it on your project that you try it on a spare hood or body to see how your mix is working first. Try playing around with your PSI vs paint mixing ratio, like everything, it's a formula that always has to be tested before finally integrating it in your project.