I vote for rebuilding your current wag. If the body is straight and the engine already has a rebuild under it's belt then you're 2 steps ahead of most people. The headliner shouldn't be too hard to do yourself and you can save some money that way. Carpet kits are easy to install yourself and you can have the seats re-upholstered to like new condition or find some used seats that are in good shape. Get those things done and detail the heck out of it and you'll be surprised how much of a difference it will make.
I also agree with Mud thrasher on the fluid's. Check and add fluids where needed and make sure your problems aren't just a simple lack of regular maintenance.
The biggest benefit to doing the work yourself is you earn a greater understanding of how the systems work, you know the quality of parts and maintenance put into it. buying another wagoneer in seemingly good condition is a toss up. unless you buy from wagonmaster which like Chaka pointed out is really expensive.