What would happen if the legacy leather got wet? I'm scared now...hahahah
I admit that I stash a plastic bag in a little makeup bag inside my nicer bags in case of rain, then I just pop the plastic bag over my bag for protection. It's completely tacky but it works. If your concern is being caught unexpectedly in a rainstorm and not being able to get to shelter quickly enough to protect your bag, I'd just try that trick rather than get another bag to carry your Coach in. It sounds a little cumbersome.
i know...I think it should be fine in the rain, but I have to admit that that is one of the best excuses I've heard yet to buy another bag!