Yeah, cooler intakes don't let the fuel atomize as well. Tommy's analogy of the iced tea glass is a good one. the fuel sticks to the intake rather than remaining in suspension when it's all cold. choking the motor just adds more fuel so at least some will be held in suspension in the intake charge and burn. exhaust heating the manifold shortens the amount of time you gotta run it richer to keep it going. A water heated manifold won't heat up as fast.
None of that is quite as bad with fuel injection where an injector is squirting directly into a port in the head.
Did they route water through the intakes to keep the intake charge warm/hot to reduce emissions once up and running? I kinda thought that's what that was for.
the recirc plates do work, but yeah, most are dead now. Adding the block off plate between the intake and exhaust still preserves some of the exhaust heating and dosen't allow a blow torch effect on the bottom of the manifold.