I've had a terrano, a alhambra and a citroen c4. The terrano was massive, the alhambra was pretty big and I'm so much happier with the citroen. The seats are a bit small in the back but my 9yo has no problems, and when she does I will swap her over with one of the dts.
It does double the mpg, and I feel more like I am driving a car rather than a bus. I still have enough space in the boot for ds's wheelchair and a bit of shopping and I plan to get a roofbox for hols. I think if you didn't need to fit a wheelchair or pushchair the boot space on it's own would be more than enough.
I would recomend the alhambra, but I'd go for a manual diesel. My auto gearbox went, and so did a friend who has a galaxy. That is a £2-3k job.