Generally enamels are single stage, no clear (not on top or mixed in). The hardness can vary but whites will usually be very hard and dark colors will usually be fairly soft. But you can't really predict it (how much hardener did the painter mix in, etc.).
Enamels don't benefit from glazes quite the way lacqers do, but I still generally prefer a glaze/wax approach over a "clean" sealant approach.
Some can be a bit fragile; if you get too aggressive and haze them up they just don't come back. Guitarman, who really knew this topic (where's he been anyhow :nixweiss), posted something a long time ago explaining how you often can't "damage the build-film", which is to say that the top surface can be like a "skin" that you shouldn't abrade too much because it won't polish out smoothly like other paints will and will also be very susceptible to UV damage from then on and could fail/rapidly oxidize after it gets parked in the sun.
That's not something that's *always* and issue with enamels, but it *can* be a potentially serious one so it pays to be careful. And generally IMO/IME the cheaper the enamel the more likely that it will be troublesome.
So don't get all aggressive without trying a test spot someplace that won't show if it gets messed up. I'd shoot for "much better" as opposed to "nearly perfect".
