@ rbentnail, don't read any of this.
Ross, there is one other way to keep your old GPS (yeah the zumo 665 is now "old") maps up to date, and that is to just partial load your local area segments to the device itself when you do the map update. It will still (always) load the entire map set to your PC, so if you later decide to go on a big trip, you can then push the parts of the map that you didn't previously load to the GPS onto an SD card using the same techniques I linked to above. Kind of a "split maps" approach.
This is probably an adequate solution for the vast majority of us who do not participate in nation-wide rallies and such since, using you as an example, living in the far NE corner of the continent, how often do you really need those far western maps anyway? And when you do you can just load them to the SD card before you go.
As for clearing the track logs, I'm in the habit of clearing those regularly. I just use mapsource (Basecamp will do it too) to pull the tracks along with the waypoints and routes I used for the tracks off of the GPS and then save them to a folder on my PC's hard drive (called GPS Tracks) with a filename that includes the date and will remind me of what that tracklog was. Once I have saved them to the PC I can go into User Data and clear the GPS of all tracks, which does free up a lot of space.
You may not realize it but after a while the GPS actually "archives" the old track logs into an archive folder on your GPS. Once it has been archived it no longer shows up as a blue line on your screen, so those old tracks are just taking up space unnecessarily.