Exit stage left!! I have to say that I find them easy to clean and I use a nice soft round headed brush to get into the little corners.
Firstly, I give the wheels a good clean with the squirty attachment on the hose, then I use a soapy sponge to clean as much as I can, especially along and in between the spokes and rims. I then use my round headed brush to get into the corners. Then I hose them off, leather them dry and polish them occasionally, which makes them much easier to clean next time.
The brush I use is similar to the one you get with Wonder Wheels, but an ordinary 1" or larger, paintbrush would probably do.
I must say that up to now I have never used Wonder Wheels, as I dont let my wheels stay grubby for long! Often if it has been raining and the wheels are a bit dirty when I get home, I will wash them off (not the rest of the car) whilst still wet as any dirt is easier to get off then, rather than letting it dry.
If you like the style, then go for them. They look great and personally I dont find them hard to keep clean.