I agree with you on this a little.
Waiting on a cacher with no email avaiable through the profile page is a long shot at best. Unless it is a old cache like a 2001 or 2002 or has some special logs that you find in need of preserving like the last cache logged by someone that has pasted or along those lines, it maybe not worth perserving.
Maybe the Maine reviewer can help with the adoption on the abanndoned ache with the cercumstances that we are working with here as posted by you. A lot more info would help.
Looks like a cacher has an interest in preserving a cache that means something to them. I say, if it's a cache they want to preserve, go for it. No matter the age of the cache or the effort they want to put into contacting the current cache owner. IMHO, it could have been placed last month and still be worth preserving if the person wanting to preserve it has a reason. It doesn't have to be a reason anyone else would use. Go for it and good luck.
Worst comes to worst, just replace the cache as long as the land owner doesn't care. You may not be able to adopt but you can replace the container at the appropriate coords and just take over maintaining it. Nothing wrong with doing that so the history is preserved.