We've had our 2004 x23B for a year now. We have 4 kids, age 10, 7, 5, and 1. Having moved up form a 10' pop-up, we got used to sleeping in cramped quarters, so we never have to fold the couch or dinette for extra sleeping space. The 1 year old sleeps with us, the other 3 kids bunk together on the other bunk. As they get older, that might change, but we'll either 1) open up the couch for sleeping room, or 2) place a cot down at bedtime in front of the couch. The x23B has worked well for our family. Things like ground clearance, u-dinette, cargo-capacity haven't been an issue for us, since we're accustomed to packing light and travelling with empty water tanks, buying firewood upon arrival, etc...but you gotta decide what you can live with... :)
As far as shopping used, there are a lot of things to look at, but first and foremost I look for a clean camper that is in like-new condition, especially inside; you can tell that it's been taken care of. Also check condition of the tires (dry rot, treads, age, etc), signs of water damage (water stains, etc), make sure all appliances/equipment work; check canvas condition. One of the big things we (and the dealer, apparently) missed was that due to previous roof damage, there was a bit of delamination at the rear left of the camper. We knew the roof and back had been replaced, and made as sure as we could that all was sealed tight and dry, but the delaminated part was not visible except in certain light and at certain angles. So...be sure to check for delamination (bubbles) in the sidewall. The dealer offered to take it back because they missed it too, but we decided to roll with it considering the rest of the camper was in immaculate shape, and based on the deal we got, worst-case scenario we trade it for something nicer and newer. Well, good luck!