I heard somewhere that you should be using material instances of a base material even if no parameters are changed to save on performance, something to do with the base materials themselves not being optimized for runtime or something. I could see how this could be miss-interpreted and just untrue but i figured i would ask and hope that someone who actually knows would let me know 
This is not true in the way you are thinking. If you compare one material to one material instance, the material instance will actually be heavier in terms of performance because it will add a draw call.
However, when you look at it on a level scale or for the entire game, that’s a different story. If you create a master material and use instances of that material to populate your level exclusively, then you will achieve significantly better performance compared to having a unique material for every mesh.
Performance wise, setting up a master material is good approach, you could also look into virtual texturing: