Do motivational speakers have an influence on our lives? I suspect they do, though it is in ways more subtle than they, themselves imagine. I look back at the hundreds of motivational speeches I've heard - and I do mean hundreds, because I've been into speaking myself for over forty years - and I find it hard to recall actual words that have left a lasting impact, though I'm sure they have. Rather, it has been the energy, obvious integrity and sincerity, which has made its mark. There is is an old saying in the speaking fraternity, we need to "Walk our talk." This means we should exemplify that which we are teaching and encourgaging. We should 'practice what we preach.'
My favourite speaker was the late Dr. Norman Vincent Peale. He did this. He was a preacher who 'packed 'em in' for years at his church in New York. Imagine that! People lining up down the street to get into church to hear the preacher. This man was a motivational speaker of the highest calibre.
On YouTube you can find lots and lots of speakers to watch and listen to. After a while, you'll know which ones are really speaking from the heart. Those who are willing to put themselves 'on the line' and take risks at being laughed at or ridiculed. Who take the risk with a sort of 'voluntary vunerablility' because they're less worried about their self-image than they are of the message they're intending to impart.
It's said that the effects of a motivational speech is usually lost on the listener within three or four days. This maybe true - except if you presented that message in a story. I know from experience that stories are remembered by audiences decades after the listener first heard them. So my advice to any motivaitonal speaker is place your message within the context of a moving story or stories. It's effect will be far longer lasting than any straight appeal which hasn't bothered to include such. Stories stick!
Good luck in your search in finding the best role models in your own quest to be a motivational speaker.