Hi and
to disABILITIES!
A wheelchair (or
ECV) will not allow bypassing of lines.
The lines for almost all attractions at WDW are "mainstreamed". This means that the queue is set up to allow wheelchairs and/or
ECVs to go through the line just as a person without a mobility problem. As it was built prior to the ADA, the Magic Kingdom is most likely to have non-mainstreamed lines. Some attractions, such as Splash Mountain and Haunted Mansion you will go part way through the regular queue and then be diverted. Other attractions, such as Big Thunder Mountain or SpaceShip Earth you will initially be directed to an accessible entrance.
All the theaters are set up with seats (usually in the back row) removed so a wheelchair or ECV can pull into a space and there will be regular seating on either side of the space for the others in the party.
Where there are quantity limits on space, or other limitation involving accessibility, you may have to wait longer to see a show or ride an attraction than people without disabilities.
The normal (and official) response of Guest Relations to people with mobility and/or stamina issues is to recommend rental of a wheelchair or ECV. The Guest Assistance Card (GAC) is intended for "invisible" disabilities not related to mobility or stamina. A wheelchair or ECV is sufficient to notify Cast Members of special assistance normally needed. However, if a person has other issues, such as auditory or visual, they would probably also need a GAC.
Note that a GAC is
not intended to allow bypassing of lines, and it so states on the card itself. The only people who will get the special Front Of The Line GAC are where a terminal or medically fragile child is traveling on a trip from Make A Wish or similar foundation.