Alan, in that case it does sound like you would be a good candidate for discs, just because of all the constant grit. As others said, if the idea appeals, then you have to start to look at all the various angles of if your frame can take them, new hubs etc etc, but perhaps a diff bike with discs would be a good idea for you in the future at some point. I could seriously see the appeal if you are doing that much rain riding.
I actually don't do much bike commuting these days. As I've said, since my employer provides a complimentary transit pass it doesn't make financial sense for me to bike commute. And since I set most of the day for work, I now prefer walking/running to biking because I don't want to sit when not working.
The bike -still only conceptual at this point- I'll be building will be mainly for touring. I don't plan to ride much in inclement weather; hopefully, I'll be able to avoid it in most cases with good planning.
So I'm mainly concerned with functionality, durability, and repairability. As I said, the reason I'm hesitant to go with disc brakes is because of my perception (perhaps prejudiced) that they're more complicated than rim brakes. I'm basically weighing the benefits of discs in terms of less rim wear vs the simplicity and repairability of V-brakes: The purported slight performance advantage of discs is completely irrelevant to me.
Right now I think I'm still inclined to go with V-brakes. Since I'll probably be doing mostly consistent riding, with minimal stop-go situations, I probably won't be using the brakes all that much anyway.