I recently read a study that the houses in Bentonville, AR that are within a short distance (I don't recall the exact distance) of their bike trail system increased in value significantly compared to the houses in Bentonville that were not as near the trails. It was quite a bit, and there were a lot of houses in that zone. I would have no problem believing that living near this trail (which I do) would add significant value to my home, and the data backs it up.

Here's a link to an overview