We all struggle with these ideas - no matter what we have now, we find many times where we want more room, or just daydream about an additional vehicle.
The Quigleys and Sportsmobiles are natural platforms to hold 6 people in comfort, and allow them to bring a lot of stuff. They are relatively capable off road, very capable on dirt roads and comfy on interstates. They usually have the suspension and motor/drivetrain appropriate for the task. For rough terrain, it isn't so much that the van can't make it, but your passengers and gear become scrambled eggs - so we need to ask ourselves is this the sort of terrain 6 people want to experience in one very large vehicle? And although they show pictures of these vans tackling technical trails, that takes a very experienced driver - when you test drive one in city traffic, they are very, very, very BIG!
The Suburbans and Excursions are less expensive, easy to find, and close in capability to the van. This depends on each vehicles particulars, but a short wheelbase E250 Quigley/Sportsmobile has much better approach angles than the big wagons, although a basic 2500 Suburban (think ex-fire department) sits pretty high and clean, compared to the 1500 with running boards and stuff.
Or, any of the fullsize crew cabs offer 6-seating, although the front bench middle is not a nice place for an adult to ride for days on end. But kids may love it there. A 4-door F250 is almost a second home.
A Land Cruiser with a third-row and off-road trailer may be a great choice - quiet, comfy human-space plus a trailer for all that 'stuff'.
Does it have to be 6 adults? 5 vs 6 makes a big difference. 3 adults can enjoy a mid or fullsize back seat, assuming the front row is 2 buckets, making a 4runner with a trailer a nice option for 5. Third row seats are hard to get into into for grown-ups.
I spent much of my youth riding around the country as a family of 4 in a Ford E150 van, and they are hard to beat as family wagons. Throw in a 4wd conversion, and go luxo with a sportsmobile penthouse top, and a big family can travel in comfort without having to tow anything. Used 4wd vans aren't hard to find, and they are simple trucks. I hope to add one to the stable one of these years myself.
m.