I have to say that I would be more concerned about how something was cared for rather than how many miles it shows. I live in the snow belt, upstate NY, and bought a 2008 FXSTC in June of 08.
Today I checked and I have just under 21,700 miles. I ride like I believe most of us do, cruise around 62-65 pass the cars hitting 80 but not for long. I've kept her clean and cared for. Switched to the recommended fluids and intervals, added a TFI fueler and Rush slip ons. This machine is the finest one I've ever owned ( 6th one ) and I wouldn't hesitate to say it runs better now than ever.
As far as worring about the number of miles, I would suggest a close inspection and a test ride to determine quality. If it looks beat up, or sounds bad chances are it is, but as in my case..She looks great because I take care of her and sounds good for the same reason. There is no doubt that she's used, but that's because ...That is exactly what I bought it for, TO RIDE.
" Roll, roll me away. Won't you roll me away tonight, tomorrow, the next day, and the next day, etc... "