Well, after much teeth-gnashing, hand-wringing, and advice-seeking (thanks to all on these boards who responded to my SS and 29er inquiries, especially Walt), I've decided to get a Surly. Not a 29er, not a singlespeed, not a road bike, not a mountain bike, but sort of all of these at once: a Steamroller fixed with 'cross tires, mungo bars, Brooks saddle, and toeclips.
I decided that I'm just not the mountain biker I used to be, at least not to the degree where I could justify buying a new dedicated mountain bike. I'm now a daily commuter, and even my 50 weekend miles are paved, with the occasional excursion down a fairly well-groomed trail. I got bit hard by the fixie bug about 5 years ago, and just can't bring myself to lay out money for a new bike that coasts.
After talking with other Surly owners (as well as the company itself), it came down to either the Crosscheck or the Steamroller. The Crosscheck only lost out because of the derailleur hanger and cable stops and rear brake mounts, all of which I will never use. (And if I decide to later, well, that's a good reason for a new bike!)
So here we go with a neuvo-retro, on/offroad, 700c, singlefixed rigid steel cruising vessel. I'm sure I'll be putting my Bianchi Pista up on the auction block once the new Surly arrives, and I'll put some pics up when it's complete. Glad to see that there's a forum in which to post them now!