I can imagine that going lighter makes sense, especially if you'll also use it for general riding around.
The reason i've leaned this was is largely due to the length of tour I have planned, around 5 months (at a fairly slow pace i'll admit) and so i'll probably going full 4 panniers.
I also want to cover all bases, I hope this is a bike I still have in years to come and who knows what i'll do or where i'll go.
Regarding the disc brakes- It seems, from what i've read and a few people i've talked to, is that they generally help with peace of mind more than anything. Knowing that if needs be, even if it is raining and you're going 25mhp down a hill, you'll be able to grab your brakes and stop whereas it seems that many cantis simply don't have the power. Though I can see that in the vast vast majority of cases, they are just over kill.
Thanks for the tips!