I've only skimmed this thread, so apologies if I've picked up the wrong end of the stick, but trying to reverse engineer a GPX file from the LOG file sounds like much harder work than starting with a GPX file and importing that into Aperture or Lightroom (which I know you said you didn't want to do).
I use a Garmin Fenix GPS watch for geotagging. It records GPX files directly and you can send them wirelessly to Basecamp. Apparently it's got some flaws if you're into ironman triathlons but for a mere photographer and general gadget fan it works well. I use a number of cameras, so with one device I can geotag them all.