Old topic, but we have to keep our wheels clean and shiny always.
A lot of wheel cleaners are not the safest for your wheels. It is too aggressive! I use natural soap in luke warm water on my alloy wheels. I make a solution in a spray bottle as well as in a bucket, spray the wheels and after a few minutes i sponge with the soap in the bucket and a microfiber cloth all the dirt away. Rinse with clean water and dry them. Cheap and good cleaner, but more important, safe for the car and the wax.
Last week i did the wheels of my dad's car on my 'natural' way, and they weren't washed for about 3 months. Half an hour, a piece of clay and some wax later they were shining as new!
When i don't have time to wash our entire car, or the weather is too bad, i only do the wheels. They are waxed with the car last October and weekly cleaning is only 5 minutes of work.