Invite your members to review any community-related events they have attended.
People that attend events love to read reviews of it. Photos and videos are great too. The reviewer will promote the review to people s/he met at the event. That’s an immediate benefit.
But you can go one level higher.
If it’s a positive review, drop a note to the organiser and see if they might send the review to their list of attendees (and sponsors!). They can also link to it for next year’s event.
If it’s a negative review, invite the organiser to send attendees with positive opinions to give their thoughts.