Quote from Quiver86
While I agree that it would be nice, I can't possibly think of any way for this feature to be implemented in his/her mod. He would have to either know exactly what mods you're playing with, the rarity of everything so a "value" can be assigned, or find an extremely clever way to do it automatically, or just assign a low static base value for every non vanilla item. So whether the item is extremely rare or extremely common you get the same bonus from it, a cheap way and probably not very good way of doing it. Or he can specifically look into a few of the popular mods and manually add in values for all the items they add in case people play with them, which would be extremely tedious I'd imagine.
Oh, I wasn't considering that, derp. I meant so that the benefits of leveling could carry onto all mod-added tools that one so chooses to put into the proper file, or against mod-added blocks. I was not at all thinking of experience bonuses, so that is a great point. Derp.