Ok... Finally got home to see what had happened... and it worked. Sort of. I had to restart Launchbox to see it, but I did have correct names for many of my MAME games... and really wrong ones for others... but that is mostly my fault for not using MAME.dat first, I believe. I am testing that theory by deleting the old MAME library and importing again from scratch.
EDIT: Ok, now I see why you don't want to have Launchbox try and d/l art and data when importing. It will get some of the names wrong, and then the importer (which is a bit of a misnomer, as far as I can tell) can't fix it or d/l the correct information. So the best course of action is to import into Launchbox without looking up stuff, then using the "importer" to fix all the names with ArcadeHits.com or whatever (which will also d/l some data, like release date and such). Using MAME.dat will only fix the names, although I've found that arcadehits doesn't always find the data you need either, so re-running the "importer" with the MAME.dat will fix any names that are still incorrect, but it will leave any that were already fixed.