chairs which act mainly as a repository for ceilidh dancers' bags, jumpers etc.

I'm wondering if there's a better way of organising dance venues?

A chair is not the best place to stash your stuff but it's often the only choice. As you point out, it isn't particularly space-efficient. And, when the dancer wants to get at their stuff, it can be hard to find unless they've carefully noted 5th chair from the left or whatever.

Personally, I'd settle for:

* Fewer chairs
* A row of (numbered) coat hooks