I maintain a workbook in Excel consisting of a worksheet for each of the cars and outdoor power equipment I maintain (my two cars, parents', sister, brother, mowers, pressure washer, etc.). I log everything - oil changes, tire rotations, transmission fluid changes, mileage. I also list the products I use, such as Havoline 10W-40 or Motorcraft FL-400S as a reference I can check before I go to the parts store.
I don't anticipate it getting me any better trade-in value, but if I decide to sell something like my lawn tractor to an average Joe, I do think it might help convince someone that they are getting a good deal at whatever price I'm asking.
Plus, I find it fun to look at this spreadsheet when I'm bored at work.