I've experimented with a lot of different gloss effects for my inner circle entry earlier this year. A very watered down ardcoat was my initial choice, but on some models appeared to streak on flat surfaces. After trying 3 different methods I found a spray gloss to work the best. It applies very evenly and smooth. Make sure you get a gloss that specifically says is ok for plastic. A word of warning though, although it looks super cool, it will ALWAYS be sticky, no matter what kind of gloss you use. I'm not sure if there's another coat you can put over it or not to stop it from being sticky, but yeah...it's kind of annoying.
These pics are from before I started line highlighting and washing but you can see the before/after difference pretty well.