One for on the bike and one for off the bike?

I try and subscribe to the idea of one tool for multiple purposes. But I've been wondering about bring two rain jackets.

If it were raining all day on a tour, my riding jacket (J & G) would eventually fail and start letting water through. It would be nice to have a more waterproof/less breathable rain jacket to wear in camp or around town or what have you. But packing a second rain jacket just eats up more space. I wonder if it would be worth it?

-Cota