Anyway, as you probably read, the main problem is that shell develops spots and welts when it rains, which can be annoying. The way to get them out is to let the leather dry naturally, then brush them with a horsehair brush for a while. You can also rub the leather with the back of a spoon, just to press those welts down. Might be apocryphal, but there's an old story about how this used to be done with deer bones (I think it came out of the John Lobb of St. James book, The Last Shall Be First). Anyway, deer bones were marketed around the shoe community for a while based off that romantic story, but some deer bones have very, very fine rough bits, which scratches leather. For a cheaper and safer solution, you can essentially get the same results with the back of a metal spoon.
To prevent spotting in the first place, you can also apply a layer or two of Alden Leather Defender, which -- as far as I can tell -- is a sort of water repellant spray. Only catch: my guess is that, by also keeping water off the leather entirely, you're also making it hard for shell to take up cream conditioners. Maybe not a problem since I'm not that convinced shell soaks up cream conditioners in the first place, but maybe something to think about. I actually sent out emails to Nick at Horween and someone at Alden this morning, asking if I could interview them for a story about Alden Leather Defender. Also looking for some people with critical views of the product, but haven't been able to find anyone in the shoe community who dislikes it. It's mostly used by that island community of Alden enthusiasts.
The other solution for rain shoes is to just spray suede boots down with a water proofer (I use Allen Edmonds). Then you get the same water repellence and don't have to worry about spotting or welting. Only thing is: you may want boots with some kind of reverse welt and rubber sole, so that water doesn't soak up through the bottom. The water probably won't migrate to your feet, but if your shoes aren't really built for the rain, the water can cause damage in the long run.