I think I'm gonna go with Nokian Hakkapeliitta R2 studless snow tires this winter at 225/40R18. I'm making plans to move to the East Coast next year and I don't want to worry about removing studs. It would be smarter to wait until next Spring to move, but I REALLY want the adventure of driving from Alaska to Jersey during the Winter in my BRZ.
Reading up on it, apparently driving through Canada during the Winter is perfectly fine and many people have done it several times. The worst part is making sure you top off your gas at EVERY available gas station, whereas in the other seasons you can skip gas stations. That's true, because I did that all the times I've been through there (three times, all Summer).
Anyways, having non-studded snow tires I think would make life easier, because even if I went late in the Winter, I'd be more prepared for any weird weather compared to rocking Summer tires and trying to go in the Spring like I did last year in my BRZ driving to the states. The R2 tires apparently handle amazingly well on ice and deep snow, but suck in standing water, which is perfectly fine since I'm not driving them through Georgia rains.
I've wanted the underbody aero panels since they first became available, but I have had to ask myself: Why? They seem much more purposeful for track. I guess I've considered them for "protection" from random road debris, but I don't really run over things. The car is low enough to the ground and I look far enough ahead and distance myself between enough cars (and the BRZ is small enough) that I've managed to maneuver around everything except broken, tire puncturing kitchen utensils next to my work place for the past 41k miles and 20 months. I don't think they help with fuel economy at all. And they're not really a "bling" item since no one will ever see them. I think they'll be added to my list of things that I'd reconsider purchasing once I'm out of Alaska.
How many miles have you accrued currently?