If you are gonna polish out aluminum, you got to stay on top of it. Which is why you dont see a lot of people running billet wheels anymore, to much maintanence. Every time mine get dirty, it gets to the car wash.

I pretty much ruined my Colorado Customs on my suburban due to the road salt in the winter as I couldnt keep up with it when its cold out. So pretty much yes, you spend the rest of your life polishing, I take my wheels off my S10 every winter and give them a good complete polish. This stuff has been around a while but I havent found anyone who has used it yet.
http://www.zoops.com/zoopseal.asp
ps, most aluminum wheels are clearcoated, except billet. So all you are doing on polishing them is polishing the clearcoat.