For the most part, forum software is just forum software - it either works or it doesnt. Unless of course someone is actually writing their own software, which I doubt very much.
I suspect the difficulty will lie with database compatabilty. A new forum would be nice, but personally I dont see whats wrong with this one really, and I think a few people would kick up a fuss if they had to re-register because the database couldnt be transfered properly.
The drop in posts might be because during weather like this, some people can think of better things to be doing that sitting infront of their PC