Another local here, I live in Delamere itself and have been riding in the woods since before I knew what mountain biking was. To be honest I can't really see how a purpose built trail would be a bad thing (allthough there has been on and off talk for years). Some of the current trails would get 'redeveloped' I suppose, but in the case of trails like the perimeter one down to fox howl, that wouldn't be such a bad thing as they get a lot of use. I assume it would be a sustainable trail, thus taking the visiting mtb'ers (And there is a lot of them on weekends) away from the other less popular 'locals' trails, which us locals would still get to keep. Trails that would be redeveloped would be the popular, and know really wide ones that 'weekenders' know about anyway. A loop out from the Visitor center to the Dirt Jumps and back could be built, still leaving loads of 'locals' trails? I think some kind of trail building on the Old Pale would be great aswell. I really enjoyed the old 'DH' track.
I do kind of agree with the 'bikes might get banned from the rest of the woods' part though
Sorry if that is a bit rambling. Just my two cents