Not too much work to polish them at all.....i clean them up real good with engine degreaser or a strong degreaser like purple power, then polish them with aluminum polish on a dremel with the small buffing wheels you can get for them. Takes about 10 minutes to do one wheel, which isnt too bad. Sometimes ill just clean them with the degreaser and be done with it, which does the job just fine but i like em nice and shiny lol. Lately iv been buying black anodized wheels from Tru Center or Douglas Q+, they are very nice quality wheels and easy to clean, no polishing needed. Those will be the wheels i buy for next year, all black.
If you want the machined wheels to have a polished finish, I can see using the Mother's aluminum polish deal....I kind of like the machined finish of the wheels. I clean them with our tire cleaner first (mild degreaser) when cleaning the tires anyway, then I'll clean the wheel with non-ammoniated Windex window cleaner. This is a good way to clean your polished wheels too if you're not going to be actually re-polishing them. Works for me.
For a show kart, there is some polish called Wenol in a tube, in both red and blue tubes, the blue being a finer polish for a mirror-like shine. That would be after the other stuff, and would be a lot of work for a race kart.
Tell ya the truth all I worry about is that the bead sealing area is clean and all I do to the outside is put some lacqur thinner on a cloth and the dirt comes right off, pretty wheels don't win races, other more important details do.