Declining numbers is unfortunate, as others have said, the information and friendships gained on this site have been invaluable. Trying to gain a larger membership by branching out to all bikes may bring about more members but ones with different views desires and agendas. More people can be a good thing, but the other side it could also be problematic with scams, viruses and other computer related information and identification stealing.
Hopefully for those in the market for a cheaper used bike, this site may see a raise in membership in a few years as the bikes get recycled to newer younger riders.
Good luck Don in your decision and thought process.