i've driven a mazda5 and it does drive/feel like a mazda3 hatch just a little bigger & higher up. i've driven a caravan and it feels quite large if you're not used to driving big vehicles. 7 seats in the 5 is nice but if you are using all 5, you have pretty much no space in the back 'trunk' area. if somehow you can fit a double stroller in there, no more room for groceries. but there's space in between the 2 middle seats for that i suppose. i guess that's why i see so many mazda5's with roof racks
i don't think a mazda5 is too bad if you don't have too much stuff to carry. i personally like to travel light anyway, and i've gotten by with an accord with my 2 little ones. but ya it would suck for inlaws in the rear seats if you drive them around often.