I also understand why some people want one...
Yes, I bought one off eBay last year for two trips (this is where I put on my flame suit.) I had back surgery earlier in the year, each trip was for a week but after the long weekend it was just me and DD. DD has a habit of crashing as soon as we get on the monorail and there is no way I could carry her, fold up the stroller, carry our bag and get on the tram by myself. I did find that sometimes the regular parking was closer in Epcot than the AAA lot.
Only once I arrived later in the day and the lot was full (MK-Saturday of Pop Warner weekend), but I typically travel during off-season.
Edit- for our trip this year, we are just parking in the regular lot since DH will be with me the whole time.