Garrabo,
The gasoline X series tractors are as a rule not as popular on trade in as the diesel, but you should still make out OK. Garden tractors, no matter how great they may be, are moving slowly at most dealers. My dealer was reluctant to take my 595 back on trade when I was pricing a 4310. He did though, and the machine sold within 10 working days. My feeling is that your best asset right now is timing. If you could hold off until early March, you could potentially trade and get a bit more money. The other thing is that you are trading for an equivalent size machine. One really takes a hit when trading in different classes. You should expect a 20% loss, realistically, on your machine. Anything less than this would be great. And yes, the 595 Yanmar has A LOT more life than does the Kawasaki gasoline, probably on an order of two. It also performs better and uses a good bit less fuel. I have had both, and those are my thoughts.
John M.