Any of these up to the larger ones are a very useful tractor on any farm, even if not used often, older, they were well made in that era and there are or were so many of that era tractor left to the wayside in the u.s. especially out west, some seemingly so as newer models came out, was not uncommon to find one that is not wore out. In this area most crawlers of that age and mfr have a lot of wear if abandoned, but not all, and you do still see a few for sale. Towing logs, heavy snow clearing, stuck tractors or set it up for tillage, wide gauge or LGP, great in soft areas if you have a pto and want to mow, they really are a useful tractor, I cannot see why anyone would scrap a good one.
The farm I get my vegetable plants from has green houses, he mostly does hay aside from the greenhouses, but he was able to afford late model equipment, all barn kept, I like the set up, his grandad started all of it way back when and though he is in his waning years now, sad to see him in the chair, he still sits outside and talks with customers, 3 generations of farming at least, and they did vegetables mostly. His grandson, in addition to the tractors and hay equipment did have a Caterpillar D6 B or C rebuilt, extensive work done, very reliable and very handy if you get stuck.
I remember all the times we used the D7 when I was a kid, now I have to get that clutch back in mine come H#ll or high water, hate being without it even though its not used all that much.