Does it enhance the quality of life for people who don't jog, cycle, or hike? Could you actually convert a significant amount of people to these activities just by offering greenbelts?
Yes and yes. One less car on the road relieves congestion for other commuters. While some homeowners may be concerned about converting nearby abandoned railroads to trails, there's no question that it will increase resale value (beautiful, quiet, paved 25 mile nature trail out my back gate? Sold!). I've seen every cross section of society utilizing these trails, including infants, elderly and severely handicapped. One worthwhile consideration: pavement is a must. Gravel roads are simply less accessible.
Sure, but are the people using them the type of people who always have? People who have never done anything like that, if they move to a community with greenbelts, will they use them?
Three weeks ago I relocated to Madison, WI which (I'm told) is one of the most bike friendly cities in the US. I haven't ridden or owned a bike since childhood, but I wouldn't be surprised if that changes in the near future. Having trails that get you where you need to go simply turns the biking questions from "how?" to "why not?". Why continue a) paying gas prices b) causing unnecessary pollution and c) sitting on your a if a bicycle can truly fulfill 75% of your transportation needs. Time will tell but I definitely think availability of greenbelts can only be a good thing.
I'm not against them, I'm just trying to play devil's advocate. I bought a bike last friday because mine was stolen before I moved to New York City. I mention this because I moved from Dallas, which is one of the unfriendlier cities for biking - the heat makes it impractical to bike to work unless you have a shower on site, and the other drivers make it a more dangerous sport than it has to be.
How close to work and your favorite play areas do you live? That's what really matters is it not? I'm betting your desire to bike is driven more by proximity first, and bike amenities second.
I actually live about 10 miles from both my work and where I play. Biking would add about 30 min to my commute each way. Culture probably has a lot to do with my desire too. Biking is almost a way of life in Madison. Creating these bike amenities would be the first step for any city to create this culture.