As the owner of a vintage rig, it's not about putting in more than it is worth. As said above that true with most any rig.
The question is: can you buy another rig that offers what you want including any repairs for less than what you will put into this one.
Tires and batteries are going to be needed on any rig - that's maintenance and sooner or later you will pay for it regardless of what you buy.
Standard maintenance costs is the same thing - sooner or later you will have to do these things regardless of the rig.
So, the question becomes is the cost and effort to get it in operational condition worth it for you? Can you do the work? Or do you have to pay someone else to do it. Can you rebuild the inside to make it a layout you can be happy in? Will the joy of the work, expense, and resulting rig be something that you love? Or will you always look at new rigs and wish you had one?
Look at the costs of a 4wd rig, slightly used and new. Can you put this together for less than that? Is the 4wd important for you?
I have put in about $20-22k, including purchase price, into my clipper. To replace it with something a "few years old" in a similar size, I would have to spend a good $40-50k on purchase alone. And, I would not like a newer rig the way I like the clipper. I would NOT be happy in another rig. So spending the money and effort on the clipper is worth it for me. I don't plan on selling it because it is exactly what I want - so who cares if I spent more than its selling price to fix it up.
It's what you will get out of it not what you put into it that matters.
