We bought a 2009 M5 to replace our 02 Explorer that was starting worry us about driving to Disney. We just returned from WDW(Monday 10/27) and the 5 is definitely our new Disney car. It rides so much better and fuel economy was about 26mpg with 2 adults, 2 kids (ages 6 & 3) and a week's worth of luggage. My lead foot probably could have gotten us even better mileage too.
The sliding doors are great for loading kids in crowded resort or park parking lots. The cargo area is nearly as large as our Explorer and I loaded the exact same amount of luggage just as easily. I was able to lay a Maclaren stroller flat across the cargo floor. A longer stroller may be different though.
The 2008 and later models have rear air and my kids were complaining about getting cold. The rear air can be controlled from the rear or front control panels.
The 5 handles nicely and can manuever between the buses and into parking spaces with room to spare. It was designed for Tokyo streets where parking is limited and very tight. Disney is a piece of cake!
Another thing that I liked was that my parents, who followed us to Disney in their car, were able to ride with us once we arrived on the Disney campus. It made dinner trips to Boardwalk and Downtown Disney very family and comfortable. I just popped up the rear seats, threw the kids back there and my 70-ish folks climbed in the second row without a problem.
I purchase accessories from a couple Mazda dealers who have parts web sites and they're much cheaper than my local dealer. So far I've bought the all weather rubber mats, rear bumper step and cargo area mat, all are well made. A rear cargo cover is available too. To date I've used these two vendors with good results:
http://www.finishlineperformance.com/store/home.php
http://www.mazdaparts.org/mazda5test.html
I researched the 5 for weeks before buying and then took my wife to see one in person. She fell in love with the practicality and loves the way it handles. I have to beg her to let me drive the thing now. All from a woman who said she would never drive a minivan!
Good luck and I hope this helped.