I have polished some small parts on my bike with a dremel and the only problem I have had is the polishing wheel on the dremel makes a fair amount of heat. When polishing a bigger piece of aluminum it's not a big deal... also, b/c of the nature of the dremel, if you are working on some pieces the dremel can kick a little and if the shaft hits the piece you're working on, it will gouge it. That's annoying.
Cordless is fair, I have a 18v cordless drill and it is good for about an hour of light polishing before the battery is too slow to be useful.
A vise and some bench mounted polishing tools will be in the garage before I do much more polishing work.