I've owned a bunk room with slide for several years with only 2 kids. Besides the obvious benefits of keeping all of their stuff in a room, they have a place to hang out when the weather turns bad. Mine used to sleep five back there, but I removed a trundle bed and put in 8 stackable 3ft deep drawers for more storage.
With a rollover sofa that converts to a full size bed, and 2 bunks, I've put up a family of 4 back there for a long weekend to Mammoth Caves NP. My niece and her 2 kids have joined us twice on month long cross county trips to the Pacific Northwest and South West. It also provides the perfect bunk house on our dirtbiking weekends with a friend and his sons.
With all that said, if all I was using it for was camping with just 2 kids, a shorter rig(26' or less) to get into smaller sites would be more convenient as I prefer rustic campgrounds. But, I always manage to find a site to fit my 33' into. Whatever you decide, getting out there is the most important thing.
As a side note; If you're planning any long distance trips, I see a F250 in your future. ;)