Last year, I traded in my 1982 Yanmar (which I bought as a "demo" way back when) YM276D, 27hp 4wd CUT on a new JD2520. All I ever did to that old Yanmar was to change the oil and filters regularly, and thats about it. All the time I had it, it was kept in my garage, and yes, I did also wash and wax it usually once or twice a year. For the most part, when I traded her in, she looked pretty much just as nice as the day I got it.
The best part, and I like to think part of the reason for it was that I kept it looking clean, was that I got roughly $500 more than I paid for it on the trade. And NO, the selling price of the new one wasn't inflated to make it look like I was getting that amount.
A little elbow grease, soap, water and wax in my opinion goes a long way in helping your unit retain it's value.
REV