I have a similar interest in light and fast touring from a backpacker's perspective like the OP. I will be using my father's 1972 Masi Gran Criterium frame built up with modern components. I plan on going backpacking in National Parks and Wildernesses that I come to during my tour and so will be pulling a trailer carrying my backpack. I looked into backpacking carrying handlebar/saddle bags and it did not seem desireable.

The OP already has a reliable backpacking setup, why not get a trailer so that you can go with what you know and not have so many conflicting requirements for the bike? Most folks with trailers tend to pull heavy loads but there's nothing keeping you from lightly loading the trailer or taking on extra food/water. Heck, I'm tempted to pull a cat around with me.