There was an article in mini magazine about it. I don't pretend to know anything about aerodynamics. But the magazine explained, that when travelling along, the air travels into the inner wings, creating an area of high preasure. I can't remember if it caused drag or lift or whatever, but the a-panel vents reduced this.
I remember reading that article, they used a red race mini & a wind tunnel for testing various ideas/myths. I was pretty sure it said it created lift under the wing therefore vents should reduce the lift & aid the air flow over the rad. I will have to dig this article out tonight.
In fact the wheel spinning round creates a low pressure, sucking air around it in. It generally exits under the car, so no point really. It's one of those, one person did it then everyone copied without really understanding why.
I remember the article showing a picture (like thermal but for pressure) about the wheels & I'm sure the front of the wheel had a high pressure in front of it. It also debunked theories like raising the back of your bonnet to aid airflow to actually suck air in, so in fact useless.
