Correct me if I am wrong, I thought you...
Correct me if I am wrong, I thought you were NOT supposed to clip the steel cable thumb loop! Metal on metal = bad?
"The C4s include a thumb loop that makes them about a billion times easier to place one handed, and gives you a second point to clip in to."
You can totally clip into the thumb loop. Metal on metal is fine as long as a rope is in the system. The nylon sling does little to absorb shock, because it's so short, so it pretty much makes no difference. That said, unless you're aid climbing, clipping to the loop will make your cam walk without fail.
The wire loop can be used as a clip in point while aid climbing to gain an extra few inches, which was not an option with the previous style camalot. That said, it should not be used as a clip in point while free climbing. The BD camalots now have a special, wider nylon sling that utilizes a frost-knot like double up across the wire loop to better distribute the load onto the wire loop. See the article titled "QC Lab - Re-slinging camalots and C3's" on the Black Diamond website for a very scientific breakdown of how this works in real world climbing scenarios.