I just moved to Twin from Boise but have ridden I.S. several times. I have always had low pro tires on my hard tail (great for Boise and most racing I do in season). They have been fine out at IS. In my opinion Noby Nics are overkill from a traction standpoint, but not a bad idea from a protection standpoint. The terrain has many long sharp rocky sections so sidewall protection and puncture or pinching should be a concern. My light XC race tires are fantastic from a traction standpoint, but wear qickly especially on the sidewalks. If budget is not an issue I think a lower pro tire like the Racing Ralph with Snake Skin sidewalls would great. Schwalbes wear fast so I would plan on a few pairs a season depending on how often you ride.
J2112 is right, most of the time the Nobby Nics are overkill but in the late season like now some of the trails get pretty loose as the trails get dusty. The rocks do chew up the tires pretty fast with the soft tread.
The rocks do really chew up the tires, I think something with a slightly tighter tread pattern would help keep knobbies from tearing up. I don't think an XC race tire is very well suited though, the terrain is lava rock and just too harsh (or loose where the rock breaks up into slippery beady bits).
I've been pretty happy with Captain Controls (stronger sidewall) or I see Nevegals/Hans Dampf type tires out there quite a bit. Needs to be harder compounds though, the soft compounds will get destroyed.