X2 on the condensation dripping on the outside. The "add on" AC unit that gets mounted under the dash, has a condensation hose that runs out through the firewall to let it "drip" outside.
As far as the hose that you see on the firewall that "doesnt go anywhere", That is the vent for the cowl. It drains the cowl vent that is mounted in front of your windshield. The thing with the slots in it mounted between the winshield washer nozzles? Yeah, thats it. Without that drain hose, everytime it rains you would get wet feet.