To the O.P. richy2,
Our rig measures 23'-8" long, and we tow a 2006 Jeep Liberty to be more mobile. National parks, monuments, forests and such is our primary focus. We have gone on one 4 week trip out west without towing the Liberty and we regretted leaving it home. We were able to get around with the house, but with limitations and inefficiencies.
Once you get near 22 feet long, it becomes difficult to get around in the places we travel to. Below that length and you can still fit into a regular parking space. That's what it's primarily about from my own experience.
It really is not that big of a deal to tow a vehicle once you get used to it. If you really like your 29 foot rig you own today, I would keep it and just tow something.
Here is our 23'-8" long rig and tow.

Something like
THIS sibling of our rig is as long as I would go without bringing a tow vehicle along.
ADDING: I can see one trip we would leave the tow vehicle home, a trip to Alaska. I would think it is more of a "sight see as you travel along" kind of trip with very little "base camp with day excursions" where a tow vehicle is most handy. Am I right????