It's obviously a personal choice. I generally don't get sentimentally attached to things like that though when someone else has stuff like that it really is neat. When faced with a decision like that I try to assess what will give me the best service for the least money. How reliable will it be and how soon will I have to fix it again? It's not just the cost but the aggravation of something breaking down. Since it broke down when you were using it you obviously need it then.
As far as I'm concerned newer does not always mean better. We can get into a lot of discussions on planned obsolescence and things are made cheaper now (I'd probably agree with both of those. As an engineer I'm often embarrassed at some of the junk that's sold these days.) But one big difference is that things are a lot more complicated these days. When I started driving cars did not come standard with air conditioning, radios, power windows, or power much of anything. Today's cars seem to be in a competition as to how much bling can they add to them. As far as I'm concerned a lot of that stuff is just something else that can go wrong. A whole lot of why cars may not seem to be made as well these days as in the good old days is just that there are a lot more things that can go wrong.
The reason I mention this is that your 70's tractor probably has very few moving parts and things that can go wrong. It's quite possible that a fix really will be a fix and will last for a while. It depends on what is wrong and what shape the rest is in. A tractor off of Craigslist might be a great buy, especially if it is an estate sale or someone is moving. Or it may be a piece of junk. Without looking you just don't know. Thee is a good chance it has more features than your old one.
It's seldom an easy choice. Twice this year I've made the decision to repair instead of replace, one a car and one a lawn mower/tractor. So far they both look like a good choice this time.
Mom's washer broke. Dad fixed it. Mom hid a few pieces to get a new machine. My dad always knew when there were missing parts. When Mom got her new washer it was because she threw a few extra parts into the pile. That did it!
