Wow!! Thanks for all the great information, you guys Things like the semantics in question are very important, as are all the types of trail (power trail, etc.) you mention.
Knowschad got it right, by the way, - we're looking at doing something like this for the Star-Spangled Banner National Historic Trail, perhaps in tandem with local geocaching groups, tourism agencies, etc.; we're in early planning stages. I can't promise anything! The area covers about 290 miles, some of which are water trails, in Maryland, DC and Virginia. I understand there are caches in many of the areas the Trail covers, so learning about "owning" an area is also really important; we don't want to step on anyones toes! Maybe we can work with these people. We get around the National Parks prohibitions because National Historic Trails partner with sites along an historic route. So, the places we hope to place (or maybe adopt or otherwise involve) cache won't necessarily be NPS land. We'll see... .
Thanks, also, for suggestions of places to see how groups or series of cache have been successfully laid-out. The Alleghany example seems really well put-together. That's the only suggestion I've looked at just yet, but will follow up on the others today.
Do you ever look at maps, or lists of coordinates for cache series? For example, if a geocaching booklet were placed at a Trail site, would you pick that up? Or is this and other geocaching websites the right venue to connect to people?
Thanks again for all your help!! If you're interested in what I'm doing with the Trail, you can always check out my blog (www.starspangledbannerblogger.wordpress.com), or check out the NPS' Trail site (www.nps.gov/stsp).