I think they're worth it. I'm not much for full on snow riding. I'll do the shortest possible route (includes use of Metro) for that. But Baltimore hangs in that 30 degree area where there is a little snow, then a little melting, then a refreeze- this is where you get a lot of wet icy wash outs on the roads. Even when they're infrequent, studded tires give you a MUCH higher level of calm when riding in traffic. And, what little they slow you down from drag, they more than make up for by allowing you to ride faster in mixed conditions.

BTW if the tires are just for commuting, I'd get the thinnest and fastest one's you can find. My recommendations are the Schwalbe Marathon Winters (NR rides them and they look like they're great tires) and I ride on Nokian A10's for a 650B wheeled bike.