I did a rough finish sanding using 100 grit sandpaper glued to a scrap block of foam. This worked great- yielded a nice smooth finish without ripping the foam. The foam didn't load up the sandpaper either. I used Elmer's glue to attach the sandpaper.
I only took the high spots off of the wing- I'm not going to try and remove all of the spanwise artifacts from the wire cutting process. I'm afraid I'll remove too much of the airfoil. I also made sure the leading edge was nice and rounded.