I vote to do anything that brings together your partners, customers and prospects, as long enough folks will come.
Sometimes even 10 is enough.
If you can get 5 customers and 5 prospects to come to a customer dinner — do it! Those 5 customers will feel appreciated, and will also help you close 5 prospects.
10–20 is enough for a dinner.
Similarly, as long as you can get enough folks to come to your hackathon — do it. Talkdesk started off an early hackathon winner at Twilio. It grew to be one of Twilio’s largest customers. That justifies it right there …