I came here hoping to find a solution to this frustrating problem, but it appears no simple solution existings.
All I would need for my uses is the ability to download an entire state at once, or at least a higher limit on the PQ. I see no reason for a 500 cache limit on the PQs. Why not make entire states available via FTP? In a few seconds I'd have all the states I needed for a trip.
The filtering I can do myself. I first create my route in Garmin's Mapsource, save as an mps file, then use that mps file as an arc filter in GSAK, using a 1 mile distance from the roads I'm on.
All it would take to make this so easy...at least for Garmin users, is access to larger groups of data, such as entire states.