I bought a pair of Mary Jane Crocs (Red) on Sunday (I had been into the shop to try them on a week before, but didn't buy them as I hadn't read this thread to know if they were ment to be worn that loose). Anyway, once I knew which size, I went in and they had a 20% off everything in store for that day only! So they worked out at £24. I had them on today and I am so glad I decided to get a pair before Florida. I have worn Jesus sandals for years in all weather and not only were these more comfy, they are also nicer looking and more shoe like.
Anyway, I haven't worn anything for years that weren't trainers or Jesus sandals (I can't wear any heel- even a tiny kitten heel) and these are the most comfortable shoes I have ever worn! I'd equate the comfy factor to slippers! I let my aunt try them on for her trip to Florida and she is going to go and get some now.
To the point: I think if you are looking to get into increasing walking in preparation for the parks then the extra money would be well spent in getting a pair before you go. That way they extra couple of quid you spend on them here may get you extra time in the park each day. Plus, you don't have to take time out to go and get them (if you are looking for a particular colour/style).