What is the point of this vent?

I believe it is to let trapped moisture evaporate from that part of the car.

It has a vent cover with a filter. Seems like it's filtering something from the engine compartment. It also vents into the passenger compartment, but there isn't a cover or filter in there.

its there to equalize the interior/exterior pressures whilst closing the door with the windows up.....

It's to let some air out with the top on to make it easier to close the door and also to create ventilation through the cabin with the top on. The inlet air in the front can't move through the car if it can't get out.
It was designed in as there was not a factory air cond. considered at the time imo. Newer designs use a rubber one way valve.
Charliew

Really? why the filter?

put some tape on it and the other one and try to close the door.

The doors are off right now.

It's a rusty mess, so it's hard to tell where it is supposed to vent. Does it just vent from the door frame into the passenger compartment? I'm wondering if I could cut all that mess out of there and run a piece of hose from door frame to the passenger area?

It is the cabin air exhaust. Fresh air fan brings in air, and it needs to exhaust somewhere if the cabin is fully closed up. This goes around the door seal. The filter is to prevent insects from coming through and setting up residence where you cannot find them.

I thought it directed air at the rear screen helping to prevent it misting up

Ah say confused-shush the piece of many puzzle always has a home!

it's there to support and connect to the tube that goes up the sail panel, that tube is there to support the foam that fills the the cavity in that area, and that foam is there courtesy of porsche to absorb water and rot the sail panel and door jam.

I guess my real question is...can I close it up?

I remember reading many years ago that this was the place where the air from the cabin can exhaust, say if you have the front fresh air vent open. It was located there because there is a low pressure area near the door jam when the car is travelling down the road, and thus you get better air flow.

I wouldn't weld it shut. Car companies don't spend $ designing worthless parts. It's there to help vent, just as others have said. Why would you want to?

air flowing by the door gap when you drive creates negative pressure which sucks out air from inside the car.
it creates circulation when air is dumped into the car by the fresh air fan or heater.

without it, no cabin air can exhaust and the fans (fresh or heat) have to work harder to push air inside the car.

Andy

Once again, Dave (as usual) has hit the nail on the head!

It IS part of the (excuse the GM version) "flow-thru ventilation" system.

Whatever you do, do NOT plug it up. The vent system will not work. You will never be able to recirculate the air in the cabin. You will die of suffocation (OK, just kidding about that).

As McMark says - it's designed for a reason. That reason is to circulate air into & outta the cabin. The "hogs hair" filter is to keep bugs from entering when that car is parked - ask me how I know!
Pat