We used to have a Fiat Multipla (6 seats) that had a decent boot, but didn't give us an extra seat for giving friends lifts when all 4 of the boys were in the car.
Then had a Vauxhall Zafira (7 seats) but not much leg space for growing children, boot not too impressive either. Borrowed a roof box to go on holiday with.
Then had a Chrysler Voyager, (7 seats) lots of space for gangly legs and a reasonable boot, but would have preferred the Grand Voyager for more space. Did invest in our own roof box when had this.
Then had an old Toyota Previa (8 seats) for a year, decent boot but not very economical. Of course, there is space inside for luggage with it having the extra seats. You can get these as 7 or 8 seaters.
Now have a Ford Galaxy (7 seats) and find the boot too small so have roof bars for the previously acquired roof box.
When between cars we hired an Hyundai i800, it was new and very nice on the inside, unfortunately it looks like a van with Windows from the outside. Not as economical as the Galaxy is though, but if money were no object I would seriously consider having one of these, got about 30 miles to the gallon, similar to the Chrysler we had.
Unfortunately when car manufacturers add an extra row of seats they have to take out space from elsewhere to fit them in, otherwise the cars would end up really long. We find the Galaxy only just fits in most parking spaces so if it had an extra 6 or more inches on the boot it would poke out whenever parked, especially in Sainsburys tiny parking spaces, and I would worry it would get hit all the time.
7 seaters just aren't designed to be used full all of the time or for holidays. I have been known to grumble to dh about the lack of boot space for luggage as you would think it would be obvious that the more people you have the more luggage you need, even just clothes, therefore you need more space to transport it.
What about buying a stretch limo?