Should pay for itself before too long through savings on heating and cooling costs!
There's this stuff called 'InsulAdd' which is a paint additive developed by NASA back in the 90s (I think) which adds insulating properties to any exterior paint. I don't know how hard it is to get hold of, or how expensive it is, or even if it's worth using in conjunction with synthetic insulation, but it is interesting! I must look into it when the time comes for me to insulate some spaces at my place...