does a belly pan help any other than air coming into the compartment ?
Well, there's that.
Plus in general a belly pan helps the aerodynamics on the underside of the chassis. Many new cars use them (I have to remove the one on my wife's car just to change the oil - GRRR).
Plus I can't count how many times I've dropped a glove in the driver's compartment while driving up to the staging lanes, and found it on the floor.
Likewise, losing my e.t. slip driving back from the e.t. shack.
Plus, plus, I have a piece of Pig Mat retained under the trans to act as a diaper for minor trans seepage drips.
Plus, plus, plus, occasionally a vital piece of hardware vibrates loose, like a terminal screw or nut.