I just did the opposite, knocking down the shine on a set of Williams heavyweight cars that made them look like toys compared to the engine pulling them. For Gloss there are a few good options:
1) QuickShine, an acrylic floor polish similar to the now-discontinued Future Floor Polish that used to be a staple among model builders to protect decals and make airplane canopies shiny. If you don't want a glossy shine, it can be mixed with Tamiya's matte medium to get any level of shine from semi gloss to dusty matte.
2) Vallejo model paints have a good range of clear finishes that are reasonably durable (mainly meant for wargaming where the figures are getting handled) but a bit of a pain to get thinned properly for an airbrush.
3) Mr. Hobby brand paints have a range of "Mr. Super Clear" finishes in spray cans. Very durable, easy to use. The only problem is that as a lacquer based clear, they are "hot" and can eat into waterslide decals if you go heavy on the first coat.
As for the rubber, my go-to is a product called Ballistol. It's an amazing cleaner/protectant originally formulated for the Imperial German army to maintain rifles, and is safe to use on wood, rubber, metal, leather--pretty much anything. A q-tip dipped in this stuff will usually restore rubber with a dry/dusty appearance. Plus it smells great.