I honestly don't know how much of a difference carpets make, I guess it depends on their design, I've never seen any carpets except the mats. But based on everything I have read probably not much difference. Foam alone does not attenuate sound very efficiently, you need it coupled with some sort of mass barrier, and vinyl appears to be the substrate of choice in most circles. Carpet is light so it cannot act like a mass barrier, and does not have construction like a decoupler (typically foam type product) so it would not act as a decoupler or even insulator really.
Also there is no vibrational dampening with the carpets. The only place I have seen vibration dampening is on the floor under your feet, at least in my car not sure it has always been there. That is what that black pad is, it is not for noise insulation but vibration dampening.
Sorry about if my last reply was harsh. It is a common expressed opinion based on my reading here that both the noise level and degree of low frequency noise (drone) is considered excessive by a large number of people who own and operate these cars, including me. I honestly don't care how loud people choose to have their cars, I just dont want my car loud, and I took you post to say that there was something wrong with someone for wanting a quieter ride.
But, it's all good, I know we'll both love and enjoy our elise's, I'll just be enjoying the radio while you are enjoying your engine growl, nothing wrong with that
2009 Saffron Yellow Elise Purist Edition - Unpurified (oem cupholder, leather tunnel cover, and black door panels), Difflow 5 element railer JR, Janspeed Stage II Exhaust, ongoing sound proofing project, kahtec blinking 3rd brake light.