I do a lot of bumpers and I usually use stripper, I haven't had one melt
yet but I'm careful as I go to watch the progress.
Some of todays bumpers have so many little openings and grill work that
I don't see how it would be possible to sand all the paint away.
I have had some "fuzz-up" from sanding when dry sanding, so I avoid that.
Usually after stripping I wet sand the whole thing with 400 just to remove
all the residue from the stripper.
Some people don't prime bumpers before painting, they just apply a coat
of "Bulldog" adhesion promoter and paint. I'll do that for small sections but
for a complete bumper I still like to prime with a good 2K.
With the "el-cheapo" bumpers I usually paint I need the 2k for smoothing
out the imperfections that they're known for.