Looks like it may be beyond wet sanding... unless your using 80 grit LOL! J/K... Yea, start over. Maybe you could wipe it with a towel soaked in thinner to smooth out the cracks then wet sand?
Just went out to the garage...and GOOD NEWS!!! Somehow, it sorta leveled out overnight. It is still a little bumpy, but now looks more like an "orange-peel" rather than the broken glass look it had yesterday. I could live with that no problem. I will put the bumper on today and start on the front one. I think the paint will serve it's purpose for the time being, even if it isn't perfectly smooth.
Well...front bumper is going along MUCH better. Just doing several light coats with 10-15 minutes between them. No runs and no crackling:bananaman Also have the AC on in the garage to keep the humidity down.