A GAC is not a front of the line pass. If your husband is in a wheelchair then you should not need a card as his will do for both of you.
He may or may not need a GAC with a wheelchair. It depends on what needs he has besides the need for an accessible entrance.
For the OP, if you haven't read the GAC information in the disABILITIES FAQs thread, I'd suggest you look there. A GAC may not be that helpful for your situation because the walk will be the same length, GAC or no GAC and many of the attractions have no place to sit.
For K Safari, there are not places to sit while you wait in line and since your DH has a wheelchair, you will need to use the wheelchair boarding area, which can take longer.
For the type of problems you are describing, WDW usually recommends a wheelchair or
ECV since a GAC will only help in lines and the walking you do in lines is only a small portion of the walking you will do at the park.
I would highly recommend checking into TourGuide Mike (a Theme Parks Board Sponsor) because his service can help you to figure out where to be when to avoid long lines. You will still have to contend with walking the long distances that a trip to WDW involves (you may walk between 3 and 9 miles a day), but it will be easier getting around with less people and you will find your waits in line should be shorter.
Also, I've seen lots of posts from people who swear by Crocs for helping them avoid pain from plantar facitis, so you might want to give them a try.