Electrification requires energy-efficiency savings. Insulation is specifically an absolute no-brainer - it's cheap and save a lot of energy (and money). Currently it seems that rentals are the issue more than anything.
There's no real way to fix that without completely stripping the house down to the frame and rebuilding with modern techniques and materials.
I don't think it does. In principle, you could stay relatively inefficient with low cost to the climate as long as you were drawing power from overprovisioned wind and solar. Of course, that energy may be better spent elsewhere so efficiency is critical, but we can't get carbon emissions down to zero by only increasing efficiency of systems that ultimately draw power from coal and natural gas power plants.