How to restore my bumpers to former glory?

[firehawk]

At least some industrial paints are available in different levels of glossiness so you could choose a semi-gloss black paint as a base. You'll probably need to add a bit of elasticity additive to it to keep the paint from flaking if the bumper gets bent or hit. Finally, some paint manufacturers have a "texturizer" additive which causes the paint to cure with an uneven surface, much like what the original plastic molded surface looked like. I think this would result in a surface that's pretty close to stock as you can get by painting.

At least Spies-Hecker has this additive which is being advertised for repairing bumpers, etc. They also have an elastic additive which is probably a good idea to use on a bumper. I've been using Tikkurila paints and they have similar products available - however, they're a finnish manufacturer so their paints may not be as commonly available.