I think Campbell and Smith in their competition engine reference manuals also suggested an exit for air as it passes over the air intake. A sole entry point showed that air turbulence increases in the ram tunneling and disturbs smooth (laminar) air flow. However, I've seen modern race cars with what looks like a ram air system (and a single entry point for air), so I can't say for certain who's right as there are variables that may work on a track car, but not be so effective for the street.
I also think any ram air effect is lost as soon as you put an air filter in the induction air stream. I do agree that cooler than ambient air temperature is better for power. Notice how much better the engine runs when the weather is cool and damp? Ask someone with a turbo how much their engine loves lower charge temperatures.
Regards,
Sherwood Lee
http://www.seinesystems.com