If the motivational speaker prompts you to take an action, then I think it does help in the long run. The motivational speaker's job is to give the listener some ideas on the "how to" of whatever they are trying to motivate one to do, and then to activate the listener into action.
A good speaker helps you to get going, and maybe prompts you along the way at different intervals (think preachers or debt free gurus). In the end, it's up to the listener to create an action and stick with it. But if successful, the listener should be able to look back and see where the motivation to start came from, and see that it helped.