IMO the "do I need a rotary" question depends on the paint. We have a few silver cars... I simply do not need one to do the medium-hardness clear of the MPV or the soft lacquer on the Jag. But on the Audis, the rotary took their silver paint to a whole new level, something I'd never been able to accomplish before. I'm still a little
about why they turned out so great, not like they were all marred up, but for whatever reason I just can't get 'em as nice without the rotary (note that I still finish by Cyclo).
But however you accomplish it, silver is just like any other color- the closer it is to marring-free the better it'll look. IME the hardest part is the *inspection*; it can take forever to evaluate a silver vehicle and all that "little marring that doesn't show" is what makes it look less-than-swell.