Yep, this is probably the best resource on the internet if you're an NSX owner. I would highly recommend reviewing the FAQ prior to purchasing the car because there's a lot of good info there.
If you're looking for an early year car, there's no reason that a 94 is necessarily better than a 91. There were a lot more 91's and 92's sold so you may be able to find one in better shape/lower mileage than a 94. If you do get a 91, be sure you're well aware of the snap ring transmission issue (covered in the FAQ). Other considerations for different years would include OBD1 vs OBD2 if you're planning on engine mods, targa vs coupe, NA1 vs NA2 (HP and gearing), etc.
In terms of winter car, you're definitely going to need something. I've got an SRV that I'm currently using as well. It'll suck stepping down to a civic from the SRV, but it'll make it that much sweeter when you get back into your NSX in the spring 
In any case, compared to the NSX, the SRV feels pretty anemic anyways, and in the winter you're looking for something that'll get you safely from point A to B. At least for me, performance in the winter isn't really a big consideration.
You can usually get a good 8 months out of the year on the NSX if you don't mind driving it in clear but cooler weather in the fall. Use the money you save by buying the civic on mods for the NSX!
EDIT: Whatever you do, don't get this beater though: http://www.liveleak.com/view?i=a52_1178712445
