The big value here is in the frame. These bikes have a large number of admirers, one of whom will hopefully come along to supply you with some broad idea of market value.
Riding, per se, will not devalue it, since frames don't wear with use the way components do. But each chip in the paint from careless handling or from the chain hitting the stay will lower its value. With a non-original fork and disappearing decals the loss of value is not on par with those NOS items that lose big value with any sign of use.
If, as you say, it doesn't fit you well I don't see why you would want to ride it except for a short spin to satisfy your curiosity.
Brent