Rain doesn't ruin shoes. It's that simple. I wear my leather shoes in all kinds of weather, never had a problem (and Berlin winters are harsh). Of course I don't hike in them for hours in the rain, but walking through the city for some hours, long subway rides... no problem.
well, it may not ruin them, but sufficient water can really cause leather soles to soften up and wear down faster ime. galoshes are the way to go i think. YMMV.