...will never shine like chrome...Just like the hub caps...
I beg to raise my hand, not to differ but to say not quite. My late model replacement OEM wheel covers are stainless steel, and when clean and polished (as they usually are) the shine is not distinguishable from polished chrome, except from an expert.
Now, before anyone gets in a tizzy here, understand that there is always a "color" difference between stainless steel and chromium. The astute will notice that; in a general description, the SS is "cooler" and the chrome "warmer". Also, the ability to polish said stainless has a lot to do with the quality of the stainless. I've discussed this before and even posted photos of a reproduction SS wheel cover, versus the OEM from MB. Absolutely no comparison, and I don't think anyone could make the former look like the latter. The underlying metal can't be changed.
There are some specialty houses out there:
http://finishingtouch7.com/How_to_polish_stainless_steel.shtml or
http://www.ableelectropolishing.com/Of course the underlying question had to do with bumpers. Surely someone CAN make SS bumpers that are high quality, and "polishable". Whether they have is another question.