So I'd keep the old steel framed bike for these mud-rides in the rain and I'd use the new bike under friendlier conditions. that's another reason why I don't upgrade the wheels-derailleurs-cranks on the old frame: I need a bike what I can use in shtty weather and on the worst road rides as well.
After all: you can't just sit on your ass and not ride just because of the weather
http://www.testbike.hu/velemeny/sarvedo/acor-afd-2503
I use it and though you need something for the front wheel's mudguard to keep your shoes from soaking, they offer great protection. And they don't have much noise nor weight, though it's almost impossible to use tyres wider than 24 mm when they're on the bike...
After all I think I'll opt for the willier, as I have the luxury of time so getting the bike is not a pressing matter, I just want to buy it now in off season as the prices will skyrocket at the spring