LOVE my Toyota Sienna.
Your kids are right - the automatic, sliding doors are cool - we get so many comments! Actually, they're hugely practical - I was going to skip them but got talked into them by my boss's wife, of all people. Can't thank her enough!
The only issue w/used is that in the early years of the current models (2003 for odyssey and 2004 for sienna and maybe a couple after), many of the safety features were optional. I wouldn't give up my VSAT (vehichle stabilty something....) - it's saved our behinds a couple of times when having to suddenly swerve on the highway because someone drops something in front of you or shoots a gap that isn't there. Also, the full air bags all the way through to the third row were not standard in 2004 - they're a huge peace of mind (particularly when my small town mother-in-law drove my kids around Denver for a week!)
as for space - we have more cargo space w/the rear seat UP than we did in a Jeep grand cherokee - crazy, huh? And w/the rear seat down, we have as much cargo space as a Tahoe (I have a co-worker w/one and I used to park next to her and I'd compare). Super, super easy to put the rear seat up and down. Also super, super easy to take the captain's chairs in and out. w/all the back seat seating down/out there's space for a full sheet of plywood (4x8). I've hauled a stove, a full-length sofa and an outdoor, wooden play structure among other things! And, we have room to haul friends or grandparents in addition to the 4 of us.
We went to a minivan when our Jeep died mostly because we couldn't figure out how to go car-camping w/two dogs and two car seats in anything but a minivan. we used to use a car top carrier when we had one child, two large dogs and went camping or took long trips (700 miles) to relatives. Haven't used it since we bought the sienna and we now have 2 kids and the 2 dogs.
Lastly, if safety is super important to you, be sure to look up both government 5-star AND the Highway safety ratings. we really like the chyrsler/dodge product when we bought (fall '03) but the driver was never going to walk again in an off-set crash and there were not air bags all the way back - made it a no-brainer to go to Nissan, Honda, or Toyota. Also, we wanted something that would go 200k or more (we buy new - but then hold on to it FOREVER). We ended up w/Toyota because it just "felt" more luxurious. My husband has to have all the bells and whistles if I make him drive it more than 5 years (they got new cars every 3 years when he was growing up!). Also, I'm short and the Toyota was much easier for me to stow and lift the rear seat - not beacause they're lighter-just the leverage was different.
Have fun test driving!