Well I got to work with my belt sander and successfully made a rounded edge triangular file. It worked great on those fret shoulders! It took me a few frets to really figure out the technique, but I can definitely see why some people like them for crowning instead of the concave files.
So after giving the frets the correct profile, I sanded and polished them from 220-2000grit and then with my dremel and some simichrome polish. To be honest, I think I did a functionally good but not cosmetically good job... I don't think I spent enough time with the 220grit removing the file marks from the sides of the frets. The tops of the frets where the strings contact are super smooth and polished, but the sides look kind of weird and rough.
Also (related), that part of the fret job sucked! It took forever and wore out my fingers, and I didn't even spend enough time to do it right. I'd love to hear the method you guys use to take the frets from crowned to playable, especially if it avoids tons of sanding with a little piece of sandpaper across the frets.