Without knowing the actual design of your system, I would still guess that the answer would be yes. Most likely, the airflow cfm coming out of each vent will be lower when you have all 4 open, but my guess is that the total airflow will be higher when you have 4 vents open instead of 2.

This seems to be subject to a conclusive answer for your space and system using only a thermometer as test equipment. No need to conjecture about it, just try it. The experiment is all but free.

Measure the temperature right after the furnace shuts off from a cycle, open the vents, wait an hour or long enough for the furnace to cycle again, measure the temperature. Done. (repeat a few times if you want statistical significance)

Do you have a return in this room? With no return, increasing supply may not make much difference.

rwiegand Said " This seems to be subject to a conclusive answer for your space and system using only a thermometer as test equipment. No need to conjecture about it, just try it. The experiment is all but free."

I like your line of reasoning.