There is a solution that could come with the advent of NextGen technologies... If instead of getting a card, the GAC were tied to the disabled individual's RFID tag, whether wristband or ticket, then s/he could be limited in the total number of rides normally experienced by an average guest during the course of a full day in the park during the season in question. The "party" allowed to accompany them could be identified in advance [with the ability to add someone legitimate in the case of a disabled AP holder] and only have access to the rides if the disabled person goes through first. This would immediately control the "renting" of GAC access to families with a paid GAC holder escort, keep the disabled from getting an unfair benefit, while they can use their access as quickly or slowly as they choose, they are limited to whatever could reasonably be accessed at that time of year by an able-bodied guest. In slow season, that might be harder to determine, I remember [without GAC] riding Expedition Everest 27 times in a single day. A separate advantage to this would be the removal of any stigma or complaints about disabled using the GAC, to any outside observer all they would see is a group accessing a ride through the FP queue. For rides that have alternate access not using the FP queue, the RFID would still be used to confirm the ride limit was not being exceeded. Whether the ride limit is used on one or multiple rides would be up to the individual, just as it is for able-bodied guests [see my EE example].
This idea would give various different types of disabilities a reasonable accommodation while reducing, if not eliminating, much of the real or perceived abuse. If it doesn't "guarantee" instant access to more rides, very few people would be wiling to pay a disabled GAC holder for the privilege, it would be harder to include a random family as part of your "group" anyway. The abusers who use it to get access to significantly more rides would be foiled. It probably still wouldn't stop all abuse, I imagine nothing could.