I always have crappy results with clear in a rattle can. I don't know if its too humid where I live or what but always get cloudiness etc. Now the paint turns out great usually, but then the clear gets messy.
I have thought about buying a small compressor and cheap paint gun to play around with but I need a bigger garage before I get into that.
Spray can clear is designed for ease, not quality. They can't have the same characteristics as solvent clear due to the hardeners mixed in, the price tag, and a few things I don't know enough about to explain correctly. The biggest thing is the price tag. Cheap is cheap. I don't know what a rattle can is off hand but I'd say like half a pint or shy of that. Calling it half a pint for argument's sake - a can of clear is like 5 bucks whereas a half pint of good clear is like 20.