so you want to replace the family SUV? or you want to buy a 2nd SUV? i'm not sure of the question. but i can give my experience.
we have 4 children (ages 1, 3, 5 and 7) and we drive/road trip/camp a lot. we also live in the country and dh is self employed as a small farmer. so we have a 2005 suburban with about 140k miles. its great for us. we need the space for road trips, we bike frequently (and since we live in the country) and take the bikes with us and we tow a (rented) trailer about once a month. I love having space for a stroller, big trips to farmers market that require the wagon, camping trips, costco and so on. since we live farther out, we plan our trips very carefully, to include many stops, so its usually a full car. I drive a little toyota matrix hatchback to work (4.5 miles away) and plan to start biking when they widen our country road to add a bike lane (coming later this year).
i think its a great plan for us and don't see us changing anytime soon. we plan to drive the suburban into the ground, and hope it will make it another 7-10 years. it actually gets better gas milage then our 1997 4runner we just sold last year when we bought the matrix. hows that for funny!
I looked long and hard at a mini van, but the cargo room is just not there. and I use my space all the time, not just a few times per year on vacation. another factor to consider is the car top and hitch mount luggage racks will really drive down yoru gas milage, so if you plan to use them all the time, thats something to consider. we have a car top carrier for long trips but we use a hitch mount bike rack, so cant' put cargo there.