We're busy, I know, but I will chime in on my question.
I haven't heard anyone who really motivated me. I've heard people who motivated others around me (Eric Maisel), I've heard funny speakers (Jenny Cruisie), I've heard pragmatic speakers (Lori Foster), and others.
But one speaker who did sort of change my life was Susan Elizabeth Phillips. It wasn't because of her topic ("Alpha Males") but the fact that I was in an audience with other writers listening to someone talk about a topic I had no idea existed. It was my first writer's conference in 2004 and I had just discovered RWA, my local RWA chapter, and writing conferences.
Her talk about Alpha Males was enlightening because I didn't know such a 'character' existed. I didn't know about hero's journeys, or GMC, or character arcs or any of that. All I did was write stories. That lecture that day was an eye-opening experience.
Four years later I'm multi-published. The first year I spent flailing around, trying to get a handle on what to do. The second year I spent polishing and honing and entered contests. The third year I published and there's no end in sight.
The moral of the story? Stay open to possibilities. If I hadn't read that brochure and paid my $85, I wouldn't be here today. Take a chance. Step outside your zone. You may not find motivation in the speaker's words, but just the fact of the speaker might be all it takes.