Well, the new MacBook Pro battery I got does not fix chronic sudden shutdown, and that's a bummer. I guess at this point my options are to cross my fingers and hope it resolves itself, try to make it happen in front of a Mac Genius so they can send it off and fix it for $350, or just replace it entirely.
If I do replace it entirely, I've decided that I don't actually need the 17" model. The larger form factor doesn't bother me, but I'm not sure that the uber resolution is worth an extra grand for what is otherwise more or less the same computer. I've been able to do a lot of meaningful development work on the 15.4", and another 1.6" won't help (that's what she said!).
So in the event I replace, 15" it'll be.