Here痴 a bit of advice that痴 helped me in my career valuing things - value the product, not the story.
One owner, washed after every use, drive it to town only on Sunday痴 - those are stories...to me they add nothing to value, just occasionally entertainment..
Need to look at what you have, a 30 YO tractor that has good maintenance records, looks great for the year and regular use on the meter.
As mentioned 2WD hurts you here, but buyers have a variety of needs - your buyers will probably be someone looking for a nice machine to mow with - and looking for a machine to handle their needs economically.
If I tossed this up against a comparable machine that痴 5-10 years newer but in average shape with same hours - I feel it would be a toss up on which sells first at the same money...anything newer with less hours or 4wd would sell first.
I personally would take 4500 if I had no use for it - it痴 fair. As a dealer, ask probably 6500-7k and prepare to get serious negotiating the first 5500 offer - it will draw attention, and that goes along way to selling something- and sitting it next to new models selling for 25k makes it look attractive price wise...but it痴 unlikely to sell in a week or even a month - and anything that goes wrong while sitting at a dealer is there headache to fix - so there is going to be markup expected.
If there痴 no rush to move, and you want to sell private party...ask 6k and go firm at 5k - your buyers probably out there. But again, Your market is price sensitive and monthly payments on new with warranty can be easier for some to wrap their mind around - even if it means going smaller or at a much higher total investment.
Or just keep it and enjoy - it痴 been well kept it seems and should be sufficient for your needs.