Without wanting to take away from your well thought out post (which I enjoyed btw), I just wanted to suggest that while halving the temperature of the exhaust gases by not insulating (to use your example) might flow double the gas through the given exhaust manifold, or to try to be more precise, double the molecules, I don't see how this will impart more energy to your turbine as it passes through it.
Double the gas taking up the same amount of physical space but at 30% less velocity? Surely this is not helpful.
..
Unless the greater density of gas passing through the turbine somehow has more torque and therefore gets the turbine up to speed faster than the higher velocity, lower density gases, in which case the only benefit of this method is faster spooling, although there is now less restriction on the exhaust side so perhaps you would have a cleaner charge in the cylinders, particularly with big overlap cams.
But I don't think it does.
Shit, count the commas!!
I know a racer who swears by the stock extrude honed and coated exahust manifold for RB26 because it (allegedly) spools the biggish turbos faster, even if it might be a restriction compared to other possibilities at higher revs. They have proven that swapping some bottom end for top end power does not always get you a faster ET.