Yes and no, the difference between running the engine even on tickover with cover up, cover down (no insulation) and cover down (with insulation) was remarkable, even quieter when driving. I'm guessing it stops any low frequency standing waves and resonances from the engine, attenuates the higher frequencies (pulley noise, air intake, injectors etc) better seal on the intersection of the cover and deck, it all adds up.
It was definitely worth doing, and being an engineer I had to measure things too 😉