As you can see in the photo, the NGK surface gap plug is holding up well. This is the first plug of its type I've used and you can see that it looks basically untouched after 30 firings or so.
I did some more testing of the igniter. As it turns out, it appears to have been running extremely rich before. I leaned it out some to get smoother operation and there is a big difference in the metal temperature. At the previous mixture ratio, the steel never glowed red.