I did the same... I don't notice much difference at all and I even installed the hot air dam which was missing previously.
I'm planning on doing the footwell and front vent mod next...
Did you make something to act as a hot air dam or buy a replacement piece? I just fixed my resistor pack problem and was going to do the insulating thing as well but that part is also missing on my car.
2005 Elise, Nightfall Blue