Well I ride Cannondales and have for years. I have gotten 30,000+ miles on three of them. Components start wearing out around 25,000 miles. Frames do not have problems in my experience and I am a pretty fast recreational rider and I am not a light weight (190lbs when I get slim).

So if the bike has had reasonably good maintenance, it still has 80% of its life on it and you should be able to get it for a better discount vs a new bike then that. The important thing is be sure the bike fits you.