I have an 1100 square foot 1980s built house in climate zone 6 with a full basement, much of which lies above ground. I have already insulated the interior of the basement foundation with 2 inch rigid foam. 

I currently have to excavate around my foundation to install waterproofing and a new exterior perimeter drain. The cost of this work already exceeds $20,000. 

With the foundation already open, would it be foolish to not add exterior insulation (rockwool, due to the prevalence of carpenter ants in my area) to the outside of my foundation? 

Doing so would add to my already pricey bill, and with the 2 inches of foam I already have on the interior, I am wondering if the return on investment would necessitate spending the extra money on the insulation and labor. I’d unfortunately have to pay for the labor, because the contractor says I’m not allowed in the excavated ditch to to liability concerns.