I did not take this path.

I know a Principal engineer who did, and he says it's been very lucrative. This was a guy who ran his own business for many years, wrote a few books and everything, before being hired as principal engineer where I worked at the time. He stuck it out as a principal for a few years before going to sales engineering.

I asked him why the switch and he just said, "You make a lot more money in sales engineering".