I spoke to someone yesterday who favors big audiences, like I do. Both of us agreed that big audiences give us lots of energy, which we then feed back to them. It's exciting and stimulating to speak to a big group. I have a big personality, and a big audience allows me to be "big" onstage.
However, this person also mentioned a couple of small presentations coming up to groups of about 25, and he felt he didn't have to work as hard or practice his presentation as much. In his mind, these groups are less important and less valuable to him than the large groups, so he tends to wing it more and spend less time preparing.
To this I say: Every audience is an opportunity to improve your skills. Every audience is an opportunity to do better than last time. (Here's an example from a previous post.)
Whether an audience is big or small, or your presentation is ten minutes or 90 minutes long, every audience deserves your best.
I understand that you might be looking for the value of the audience to your own needs -- future bookings, new connections, potential clients, career enhancement. Which is probably why you agreed to the speaking engagement in the first place.
But don't forget that your primary purpose is always to give value to the audience.
Stop thinking about what you can get from the audience and start thinking about what you can give.
And if you, like some people, feel that a short presentation is less desirable or valuable than a long presentation, again, remember that it's all about value. You can give plenty of critical tips and information in a ten-minute presentation. Your audience doesn't care what else you know. They care about what you're there to tell them now.
Don't waste time talking about how much more you could tell them, and don't waste their time by throwing together something quickly and thinking it doesn't matter.
Every presentation is an opportunity for you practice your skills, understand audience dynamics, try out new stories, experience different venues, get used to different time frames, grow your strengths, and learn from your mistakes.
No audience is less valuable than another. No presentation is less important than another. Every presentation is an opportunity to improve.