I can never fault anyone for not wanting to speak at a SharePoint Saturday event. There is no obligation and no one should feel pressured.
I have been to several SharePoint Saturdays and loved them all. They are fantastic.
The organizers are heroes to me. The time, effort and personal expense is staggering considering that there is no guaranteed payback.
Jumped the Shark? I dunno. I sure did like the ones I have been to. But then again, maybe they were better before I started going to some of them.
It's a worthy discussion, but I think it's a pretty easy argument that they are valuable to lots of people who attend. I can't be sure of the value that speakers and organizers get out of it, but I sure do appreciate it.