I have to say that I prefer the approach Darren outlined, mostly because I use a lot of ClipWrap, and I do that for two reasons.
1) Makes skimming through clips in an AVCHD on the Finder level far more manageable. The QuickTime interface for AVCHD folder structures is very poor. It’s fine as it is, but the simple fact that you have to start from the beginning to go through clips every single time is really bad from a time-management perspective. So it’s nice having a straight up listing of QuickTime files that one can easily parse through.
2) As far as I know, FCPX still cannot correctly interpret 30p footage from a Canon C100 (it’s 60i with 2:2 pulldown applied but the flag for the pulldown is wrong or something). I do a lot of 30p work, so this makes sure I don’t get any interlacing.
So ClipWrap the AVCHD archive, then use the Better Finder Renamer. I totally sympathize with the annoyance of 0001, 0002, and so on naming convention of this format.