An interesting debate, everyone. Like most, I agree with the main concepts here (I teach Physics) that increased Surface Area does not affect frictional force; increasing SA decreases pressure, reducing the frequency of microwelds.
We do laboratory tests in my class (not with tires, but with a variety of materials, including rubber) and the average results over many trials and groups indicates no change in friction by changing the SA by doubling or even quadrupling. Changing the normal force (weight), on the other hand......
On an anecdotal note, I have some huge tires (315/35R17), or 31.5cm wide, on my mustang. Just for looks - not for aero or friction for sure. I get all sorts of comments about how it "must hook up good" and I can't take time to correct everyone. It hooks just as well as the stock 245 tires I had. Maybe worse, I think these tires are harder. When it is raining, though, I can get sideways on the freeway if I hit the throttle. Then I wish for skinny tires.