The bike simply feel a little more nimble to ride, a 650b with 42mm is the same as a 700c with 23mm, so with 38mm tyres, you'll benefit from a slightly lower BB, which in itself not a problem (even with clip and strap pedals).
it's cheaper than having to get a winter bike, or a different frames.
Interesting idea, Ed. Do you think it would have much effect on the handling?