OK, she's finally fixed. Just finished up. Well, I didn't put the trim back on yet, but that can wait.
The best advice I found on the internet for getting a seat out was to hammer the wrench in a bit to get a bite on the seat. I thought there was no way it was coming out. It required a bit of oomph, but she came out, and wow was that seat trashed. It got to the breaking point last night, when my last piece of valve stem busted off with the vise grips, and I had absolutely nothing left to grab on that was exposed.
Here's a picture of the aftermath for your amusement (ya think I need a water softener?)