I run E85, so it's REALLY hard to get a read on the plugs. I use the plugs to read timing, but that's about it.

You can read fuel on the plugs, you just have to be dilligent about cutting it off at the stripe, and not driving it back. Makes for a pain to do it. Plus it only shows you what it did at/near the top end. It won't tell you want it did at the hit, or at the 1/8th. The wideband will tell you the entire run worth of info.