Two things to consider: One, as much as I like my ZTR it doesn't ride as smooth as a tractor will. Some of the new models have a decent suspension to help with that, but if you happen to have back problems, be sure to run one around the dealer's yard to see how it soaks up bumps just in case.
Two, it's not just tractors or trucks, it's everything. A couple of years ago I went through a series of buying and selling welders as I upgraded. I bought one, cleaned it up, used it, found a newer model did the same and sold the first one. I kept track of new pricing because the used machines were bringing about 50-70% of new as long as they were pretty nice. As an example, I had a Miller Millermatic 252 and those were selling for just under $3K out the door (no bottle). That exact same machine is now $4,300....two years later and a 40% increase.
The thing is, used prices went up the same amount give or take. A few months ago I saw a Millermatic 252 at an obscure auction not far away. I put a lowball bid in on it before I went to bed and the next day got a note that I won't if for a ridiculously low price....no idea how that happened as they usually draw serious money. It had the original manual, a full 330cu/ft bottle of 75/25, original sales paperwork on it and cleaned up to literally look like a new machine. Sold that thing in a day or two for $3K.