Instead of searching for concepts you think will inspire an audience, involve them and guarantee success.
As always, for workshop activities to be successful they need to be relevant to the audience, so do your research!
When a motivational speakers presentations are all centered on their own stories and analogies, it leaves a very important element of a great motivational talk out, the audience.
Below are some great workshop activities I have used as a motivational keynote speaker, with a larger audience upwards of 1000 people.
A simple activity. Make eye contact with an audience member and clap your hands in their direction. Once they "receive" the clap, They must make eye contact with another audience participant and send a clap on to them. This clap carries through the crowd. In the meantime you may start another clap in another direction and watch how the chaos unfolds! This is great for developing communication skills, interaction, getting people to pay attention, non verbal skills
Have audience members stand back to back with a partner beside them. Call out different dance styles like country western, ballet, tap, Hip Hop, etc. Delegates must dance back to back to the different dance styles. The theory is because their backs are to each other, participants will lose their inhibitions and really cut loose. Keep it quick and simple and tie it into the motivational talks theme and main points.
A motivational speakers favorite activity is to get the audience involved and inject some levity. Audience members all stand and use the sway of the hips to spell their name. (Some people get confused, how do I dot the i- or cross the T?)
Today it is harder and harder to get and keep someone's attention, especially in a motivational speech. Busy, distracted audiences in a large crowd will not put up with a non congruent message that doesn't get to the point and bring clarity to the topic. A smaller audience may be a bit more forgiving.
I was a motivational speaker for a real estate conference where I suggested realtors are on their feet delivering motivational speeches every day. In this group many of the realtors are also addressing large audiences of people to help them purchase properties or explain the real estate industry.
From a motivational speaking stand point; addressing a larger audience is very similar to addressing a smaller one but keep in mind the following adjustments.