Looking at a 2004 Ultra with 21,000 miles. Is that too many miles on it to consider buying it? How many miles should I expect to get out of the Ultra before I have to invest more in to it?
That's about 5k a year which isn't bad at all. With a good maintenance schedule, you should get many miles out of it. Just keep a check on the cam chain tensioners starting at about 25K miles and then again every 20K or so to see the pattern of wear. They all have the same problems with the TC engines and the tensioners.
If you neglect to check them and they go out on you, you may end up getting a new engine.