As to shininess, not that I exactly recommend it, but you could regularly wipe it down after playing using a kitchen paper towel instead of a ‘lint free microfiber polishing cloth’ (or whatever they’re called).
The paper towel will leave little micro scratches that add up over time and eventually leave the bass without that "Mr. Clean new polished linoleum" shine, but also without any particular damage to notice. Just an idea...
I wonder if using just a regular old shirt would eventually have a similar effect, but with even smaller individual "micro scratches" than those that paper towels leave?
Anyway, or, just wait. Plastic constantly (if slowly) outgasses and eventually shows the effects of no longer being new. Meanwhile, sunlight accelerates (slowly, but relentlessly) the degradation of plastic