This is why I've never understood why some folks suggest that lighter builds are preferable. Lighter does not necessarily translate to better tone or better sounding, and tone is what we're really after (I think).
I wonder that too. Theoretically, since the sound is coming out of the top mostly, I would think that heavier wood generates more sound. There is probably some sort of a scale that shows volume per thickness, and there is some sweet spot in there... but the wood makes the sound, so trying to minimize how much wood is there seems counter productive to sound at some level.
I guess is depends a little on what you do. If you play mostly standing, and your guitar is plugged into the house PA system, so the tone is somewhat compromised anyway, then maybe a lighter guitar that has a good pickup is what you care about.
If you play seated, and unplugged -- or mic'd -- I'm not sure why weight would matter at all, and tone and natural volume matters more than anything.
Besides, weight is relative. I played my Savoy a lot when I first got it. The first time I picked up my D40C after that, it felt as light as a feather!