I used Duplicolor paint and topcoat on my Carter helmet. I never got a chance to wear the helmet around because I was never happy with it, but I was very happy with the paint-job. Will it offer the level of protection you're looking for? There's only one way to find out...
I was going to suggest the same thing - automotive clear coat. How strong is it? The same strength it would be on a car, which endures a lot more than your armor is likely to. I painted the dragon heads on my Gene Simmons boots (and the torso and arms armor) using automotive lacquers with a sprayer and after 20 years they still hold the same color, still as shiny when polished up, and have no chips, scratches, etc on them. They are metallic silver with clear top coat. The dragon "teeth" on the platform soles are also painted, and (being closest to the ground so receiving the most wear-and-tear) they also have no marks on them. Bottom line: automotive paints are WAY more durable than counter aerosol spray paints.
Thanks Carpathia and RobotChicken. I'll try some on one of the shoulder plates and see how it goes. I noticed acrylic paint takes a LOT longer to harden and you can't even touch it with a finger for at least a couple of days!