In the thread where this was originally brought up, the consensus seemed to be that the aluminized layer really doesn't add all that much to the R value. We really can't say "If it worked for the NeoAir, it would work for the ProLite" since we don't know what the NeoAir's R value would be without the aluminized layer- most of the NeoAir's R value is from having discrete chambers of air, isolated enough that convection is slowed down so that the top layer of baffles can retain warmth without constantly losing heat to the ground.
Let's just say this- if most of the NeoAir's warmth came from the aluminized layer, CD wouldn't have bothered with the complicated triangle baffles. It would have been a POE Ether Compact 6 with an aluminized bottom. It would have cost a lot less to engineer and make, that's for sure!
I also recall someone (Roger?) saying that because of the lack of line of sight within a foam pad makes an aluminized layer even less potentially effective.
Don't mean to be a wet blanket, no disrespect! You could test out this idea pretty easily, and if you see results we'd all start campaigning for you. Or, you could sell the idea back to CD. :) Adding an alumized fabric to the bottom- or even a layer of aluminum foil- is something most of us with an iron, scissors, and glue could handle DIY/MYOG.
Even testing relative R values is something you can do without an expensive data acquisition setup. I think I've even see articles or threads here where someone has done just that. Take a used ProLite, cut it in half, give one the shine, the other not and test away!