Like the idea, feel like you need some aspect that helps arrange a group for these types of trips. I really want a small group whatever deal where the first guy or two to say "I'm in" gets a discount.

Do follow the other fellow's advice and try validating your idea on craigslist, couchsurfing, meetup, etc. We don't have a real website yet, but we've surprisingly got some leads through those channels.

You may also look into trying some of the REI trips that sortof do this already.