Yes, if you were to spend more time riding out West than here on the East Coast I wouldn't hesitate recommending NS over B-Pro. I think beyond a shadow of a doubt that NS can handle softer groomers and powder conditions better. Let me put it this way: provided you were to ride our icy crappy East Coast conditions B-Pro wouldn't revolutionize your riding, but you'd be really glad you had it 2/3 of your time spent on a mountain. In abundant fine powder of the Rockies that serrated edge is just not needed most of the time. Sure, there're icy conditions out there too but an advanced rider such as yourself should be able to handle them with just a good deck and a sharp edge.
About that agility... well, yes I do feel that the stability gained with Magne-Traction edge and wider waist actually takes away the playfulness. You will find that it is harder to make quick sharp turns. At least until you get used to the board. I ride moguls a lot, I also ride trees a lot - the B-Pro is definitely more of a workout there. Basically, B-Pro is kind of a board that needs some getting used to, but once you do it is a fun, stable and poppy board.
If you're going with any other board than GNU go with NS. In my opinion NS is superior to Arbor and Rome, They're incredibly damp and if you ride trees you'll be glad for that indestructible sidewall (I split my Jones 2 years ago running into a tree, and those are notoriously hard to break). And if you decide to go with NS go with Lotus, not Infinity. Unless you plan to spend some considerable time in the park. I just got my Infinity but I was shooting for a softer, more pliable all-mountain board that I can take to the park.