iTunes Gapless Playback – Fix iTunes ‘Determining Gapless Playback Information’ Loop

Generate a system report (in Lion: About this Mac-> More Info -> System Report, or do a Spotlight search for System Information if you allow Spotlight to index applications.)

Click on USB; then look for the bus ID mentioned. Under that bus, look through the Location IDs of each device; this field is "Addr" in the error logs. Note that location IDs are unique only across a bus, not the entire system.

Once you've identified the device, I would try swapping it to a new port, either with another device on the hub or to a blank port on said hub. If the errors stay with the device and not the port, my next step would be to plug the device into a direct port or swap cables. If you still have issues with the device, look for firmware updates to the device.

If after troubleshooting the hub is suspect - note that some people have found the power adapters that ship with some cheap USB hubs to be very poor, not capable of delivering anywhere near enough current. http://hackaday.com/2012/01/06/running-the-numbers-on-a-cheap-psu/

I would put the phone and garmin charger directly off the Mac's USB ports; among other things, your mac can supply twice as much current to your phone for charging. See https://support.apple.com/kb/ht4049

I would suggest a combination of your first and last ideas. You could re-add your Music folder to your library, and then use a script to change the location of the old entries (correct metadata) to the new entries (correct locations).

Pseudocode rough draft:

for every song in the XML file (seek)
  search the rest of the XML file for other songs of the same name
  if only one is found (found)
    log seek's name to file1
    if found is newer than seek
      copy found's Location value to seek
      remove found
    else
      copy seek's Location value to found
      remove seek
  else if more than one is found
    log seek's name to file2 (for manual editing)
  else (no others are found)
    log seek's name to file3

This script design would assuredly be quite inefficient, but it would fix most problems itself, and you would (er, should) only have to review the songs with more than 2 duplicate versions.

See this answer for details on how to make these XML changes take effect on your library.