I'm not familiar with the GR 2020, but I looked it up and it is just a good sturdy lawn tractor. However, at $9k, it seems a bit pricey if all you want to do is mow the yard, and do some occasional blading. I agree that the new Cub Cadets aren't the same as some of the older models. I have a couple of neighbors who have newer CC's, and they both have problems with throwing the deck belt. You might want to check out the Husqvarna mowers....mine is doing real good after 2 years, and I only paid $2k at Lowe's. Even if you went for the top of the line Husq, with attachments, you would still be way below half of what your GR quote was. If your Cub is still in good shape..no rust, etc., you might be money ahead to just put a good engine in it, and keep it.
Thanks for additional thoughts. I checked out pictures of the GR2020 and it looks ok, but has lots of plastic on it and just reminds me of the Sears Craftsman that my Mom used to have. As you say, it looks like a lawn tractor. I always thought of my Cub 129 as being substantially more than that. I will take a look at Husqvarna, being that several people have suggested this to me.
The Cub has no rust..is quite solid for its age...with the only main issues (besides the engine no longer running well) being a constant but fairly minor leak from the transmission, a drain plug that has had issues with some leakage over the years - actually I think this is the third plug to go in there, and, of course, a good amount of oil consumption (which would likely be resolved with a rebuilt engine). Other than that, it has been holding up pretty well. There is some play in the deck spindles, but I guess that is to be expected after 40+ years.