I have these on my car... I tried to remove the one on my spare. The clips on the outer side of the plastic come off easily but the inner side don't. I came to the conclusion that they were a once only fit and removal would mean breaking them. I guess if it's the spare it wouldn't hurt too much as a trial for the rest.
I'd venture that the main reason why they are there is to keep nasties from getting into the callipers. We had a rock find it's way between the disc and a pad on our commodore, ground a nice groove in the disc that was too nasty to be machined out. The other point is the rotor will be nice and rusty looking. This is not something I'd like to expose to sight! I guess it could be taken off, sanded and painted a sexy colour.
This is not the 1st time I've posted this picture, but is this the cover you're talking about?