Our B-25C has flame dampers too. The square bumps on each nacelle are the exhaust fairings, designed to remove the flame glare. Before those were put on (so I've read) they were so visible that night missions were banned on the early models.
So, doesn't matter if they FLY at night. I see it as a valid part of the plane, even if flown in daytime. It's not like you can just take it off when the sun rises.
Is it representative? 1/3 is a pretty big chunk. Sure, NOT having them would be nicer, but I think the uproar over them is a bit overblown. It might be nice to (eventually) have an earlier model WITH the dampers, and a middle-to-later model WITHOUT them.
It would make them a little more destinct from each other (assuming we ever get more variants of the mossie!)