As a rule, with crawlers, you can easily invest more than its actually worth or what a buyer will pay.
When terms like restoration are defined, it can have different meanings as well, which to me should be categorized, in general terms. A complete disassembly,inspection of every part, rebuild/replace as required to meet new specifications, including finish all the way through to completion, to me would be a total restoration with the end result of a completely overhauled tractor.
Something more feasible, would be going over all components of the tractor, do any necessary work to make repairs that would make the tractor field/work ready, re-setting the hour meter, not as if new, but close and it has the ability to provide considerable hours of use with routine maintenance. This can include a nice finish or not, but it has to be mechanically sound, no leaks, no repairs needed etc.
You could go over that crawler, measure up the undercarriage, see how much wear is on it, leave as is, rebuild to new or rebuild it to provide significant hours. Its possible that what you spend could vary, depending on how far you want to go with it, the present condition and what it needs to meet the above or similar. Its possible to reduce costs in some cases and not be excessively over the general value of the tractor, or what someone will pay, however with most of this old iron it generally does not happen. 1200 original hours if true, depending on what the service life it was designed for, might help, vs starting from a completely worn out tractor needing a ground up restoration to even work.
This is subjective, obviously, and like was stated above, you can easily get in for a lot more than you will ever sell it for. By the same token, you build something be it a total restoration, or whatever degree of restoring you do, there is value in the work it can do, so some will do just that. I have a friend with a D6 caterpillar, B or C series I forget now, but he put quite a bit of money into it, but it is for his farm, some enjoyment and or what have you, and he does have some acreage, greenhouse operation and does a lot of hay. Last time I was there one of his tractors was stuck near a pond, a neighbor came over with a 966 loader, but that D6 was ready and willing in the barn just the same.
I would agree, you'll potentially get top dollar for one that is done correctly, mechanically sound and aesthetically correct over one that is of unknown condition or appears to need any varying degree of work.
I prefer low hour machinery, if can be found. At the beginning of last summer, I bought a late 90's low hour ford tractor, something I have needed for years, its relatively clean, been inside most of its life, but it did need a lot of little things. Some not so cheap, but within reason, after going over it, making necessary repairs, even some paint/body work to the tin, but not the major castings except neatly done with touch up, most still looks new, I would not lose money on it. I can't say I'd make a huge profit, but given what it is, its fair to believe you could make a small profit, because its a desirable and well proven model with many years of good service left in it. To the right buyer its a worthy investment. I'll likely not sell it until its necessary, when I am too old or its not needed, I know pretty much what I have by now and as a buyer it was well worth the investment. Apples to oranges as far as crawlers and ag tractors go, but the philosophy is the same on how much you invest and what the market will bear at selling time.
Whats in the photos above is not likely a common machine, so once done, its going to be what a buyer will pay and you sure as heck would highly benefit from knowing that before you sink a dime into it LOL !