I have three older Craftsman tractors two of which are running very well. I think when your talking about any tractor you need to concider the models. I am sure that some are not as good as others. When I purchas a tractor I always want a garden tractor vers a lawn. The garden tactor will have heavier accesories such as rims, transaxels, batterys, axels etc., and this will tipcally make the difference on how long they will last. Yes, as they age you can expect to replace more parts, but this is not what I would consider a problem. Like anything if you want them to work and run properly you must make the replacemnets. However, one thing I have always tried to do is make my own replacement part when possible. An example is the steering drag link on my "96" GT, the original has threaded ball studs and though normal wear they fall out. One quick fix is to weld a washer in place to hold the ball in the shaft. After doing this a few times and not satified with the amount of play I found a type of ball joint from MSC that I thought would be acceptable. The original rod was shortend to allow for the extra length and then drilled and threaded to accept the new joint. This has worked out well and sould last the life of the tractor but if necessary a new joint can be purchased and replaced as needed. The other change from original which is probably not better but equal is to turn a new disk brake rotor. Of course you need to have the equipment tlo do this.
One other item that needs to be addressed in this vintage tractor is the steering wheel shaft. This has nylon bushings and once worn allows for too much steering play. In my case I expect that I'll need to fabicate a new shaft and insert either ball or bronze bearings. Any slop here will translate into too much freeplay in the steering wheel. I expect that the "89" Chraftsman II that I also have has the same design flaws since thay were both built by Roper.
These are a few thoughts regarding aging Craftsman tractors.