I know your pain. Once upon a time I towed a 36" TT with a V-10 and a 7.3PSD Excursion.
The X and TT was a fantastic combo. However the kids eventually outgrew the TT and it became time to upgrade.
The most economical choice and the only current vehicles that compare to an X in terms of towing ability,3rd row seating and passenger space is a van.
If vans are out of the question your next move is a Crew cab pick up.
I currently have a crew cab pick up. While I enjoy my combo I still miss the passenger space of the X.
If you go crew cab be sure to get a front bench seat. You will want the additional seat space vs. a storage console.
I suggest a dually which will allow you to get any Bunkhouse fiver you want.
A SRW truck has lots of 5'er options but at some point it will limit your selection and you will face the upgrade game. Get the dually and you will not need another truck for a long time.
I'm not sure I would go to the expense of a body modification.
A family of 5 can fit into a crew cab truck. It will not be a spacious as an Excursion but neither will your extended crew cab truck.
You mention you only camp 3-4 times a year. That is a big issue. Are you really going to invest in a new truck RV combo for 3-4 trips? If you're only going 3-4 times just buy another X. They are out there still. Just get one with more life in it than what you had.
If you're ready to do a lot more camping gravitate to a dually and 5'er. If you are not ready to make that commitment stick with the Excursion. There is no other vehicle quite like it.
The 3-4 trip thing is really the sticking point. If you are only going 3-4 times a gasser will do. However if you are going to commit to more camping invest in a diesel and don't look back. I would certainly opt for a diesel vs. body work to extend passenger space.