I was thinking, can't we get random monster units as we go up Adventure tech? Not as a tech in itself, but as a result of going higher, you just get higher chance of a random monster joining you. It might add some uniqueness to the Adventure tree.
Similar ideas could work for the others. Warfare, for example, the higher you tech, perhaps the greater chance of getting bonus to attack and defense or something. A reward, if you will, for focusing on one tree, and a benefit for teching in it at all.