How chambers prove the value of membership

The renewal conversation
Membership is sold on access to people. When renewal comes around, the member tries to recall what that access actually produced. If the honest answer is a few pleasant evenings they cannot reconstruct, the value was real and the evidence was not.
Attendance is not the metric
Counting bodies tells you the event happened. It says nothing about whether anyone got anything from it. A director who reports attendance is reporting effort, and effort is not what the board is asking about.
Make the network visible
The strongest renewal argument is a member opening a directory and seeing the people they have met through you across a year of mixers. That is not a claim about value. It is the value, sitting there in a list with names and faces on it.
One directory, every event
Individual event pages help for a week. What changes the renewal conversation is continuity across the year, so a member sees an accumulating network rather than a series of unrelated evenings they half remember.