I also have terrible PF. I had cortisone shots right before our last trip (including on the day before we left). I have Crocs and they are ok for everyday walking and are especially comfy for around the house--but I can't imagine wearing them all day for all the walking at Disney. Even wearing them for an extended
Walmart or Mall trip leaves me in lots of pain, and they rub other parts of my feet and cause problems. I have prescriptions orthotics and good tennies for that. But even then I have a lot of pain.
Make sure you try out Crocs before you take them--they just don't work for everyone.
Some things that did help last trip. I bought ankle supports (over the counter at Walmart type) that adjust with velcro over the top of the foot and the ankle. I pulled them tight across the top of my foot so there was lots of support to my arch and the PF area. This helped some. Also volunteered to push my dd stroller at all times. Just having that little bit of support to hold onto and take the tiniest bit of weight off my feet helped--like using a walker!
The biggest thing though that I recommed for now is to get a night splint. Your podiatrist can get you one, or you can order it for yourself. It is really awkward to sleep in, but it really does help--A LOT!
The catalog
www.footsmart.com has a lot of speciality products for PF--including night splints and PF support items. Night Splints aren't cheap, but they are well worth it. Over time it will help to heal PF and will make you more comfortable overall.
I am dreading my next trip because I will be by myself with my kids. They can't push me in a Wheelchair, and I think I would have problems using an
ECV and keep up with them (DD always wants to hold my hand). Plus I am a go, go, go kind of person and and ECV would really cramp my style

I am hoping for the best and planning to just take lots of breaks. The worst for me is just standing in line. I am just miserable when my feet hurt that bad and I have to just stand for ever. Since it will be Sept I am praying for the low crowds, and planning to take advantage of EMH and fastpass.