Jon is right. The only wetness you want to feel in the winter is from sweating. See
http://www.seagrant.umn.edu/coastal_communities/hypothermia for why.
If you are paddling in mostly calm water where your are unlikely to find yourself tossed about in waves or surf, then you shouldn't get too much water penetration from a good neoprene neck. Of course, that means that when you really need it, the gasket will probably fail....
Some of the semi-dry suites with neoprene neck gaskets probably work OK. I paddled with a IR dry top that used a neoprene neck gasket for years and it never leaked. However, it was billed as a dry top, not a semi. I also never used it in really cold conditions, I used a dry suit.