I think that Chénier is actually advocating a "research" element to the game, where an investment leads to a permanent increase in productivity.
That would be neat, but would mainly help regions that are well-sheltered from invading armies. My region of Raviel, for example.
Not really, I don't think permanent boosts would be in any way balanced (unless they work like other buildings and can be looted and have upkeep? could work too I guess...)
I just had in my mind stuff like paying to have massive irrigation pipelines built, or new fancy mills and the like, which would deteriorate because of use and production would therefore return to normal after a short time like it does now. Mind you, agricultural infrastructure sounds like a good way to go ahead with this too, and could be rather interesting. Right now, building warehouses are our only options.
