So I pulled my rear fascia off to find that a staggering proportion of the little pop-in rivets that hold the fascia to the mounts are broken. Anyone have any suggestions for replacing them/strategically eliminating some of them?

If you're referring to the black plastic fasteners that run across the bottom of the fascia and across the top, underneath the tail lights, try this site on page 2, ninth item down. I don't have one to compare sizes, but I think it's listed there. http://www.clipsandfastener...d_Fasteners_s/64.htm

They are common GM items, so you might be able to get some at your local GM dealer body shop or automotive paint and body shop.

Lowes usually has a selection of these push rivets

I just found one in my parts shelf. It has a 1 inch head and a 3/4 inch shank, so the one I indicted should work. Fastenal may, and I say MAY, have them. I personally haven't found my local branch to have much of anything.

The Fiero Store carries a selection of rivets and tools if you can't find them locally.