AFAIK, less wires means more sound from the drum, more wires means more buzz. 20-something is supposed to be a blend of drum and buzz. Its nice for wood snares because ... the reason why you got a wooden snare is the nice warm tone of the drum. And you wouldn't want to drown it in buzz, right? But for steel snares that have a "boingy" shell sound, 42 wires gives it a "thicker" buzz sound, which compliments the "boing". That's why I use a 42 on my steel drum.
Oh, and BTW, I like sympathetic buzz. I read in many fora of people who try their best to kill sympathetic buzz when they hit their high toms. But I love it. It adds harmonics and overtones to all the drums from the toms to the kick. As I said earlier, 42 strands sound "thick", and the resulting sympathetic buzz is likewise.
But that's just me.