OK, yeah, depending on what kind of crap (and how much of it) gets stuck to the front of the bumper cover I can see your point. The glaze will hold up for a while though, so unless you get some nasty bugs or something you'll be OK with once a week or so.
FWIW, I put some #5 on Accumulatorette's freshly painted front bumper cover before she took a roadtrip to Dixie. When she got back (ten days and many miles later), everything cleaned/clayed off just fine with no etching or other problems. I was worried about the bug-guts, but they didn't hurt anything.
