The 'value metric' can be a seat-based license. It simply means that you price the seat based on the value it brings to the customer, not based on a cost+ (your costs plus a margin) valuation or a competitor- (your competitors price minus some amount to make you stand out).

I think you're confusing "value-based" with "metered". There's another model which is a hybrid model, not strictly metered, but not strictly seat based. An "hourly package" like gitlab-runner minutes is an example. The trick is that you can incentivize usage by giving them leeway to exceed their per-seat cap without penalty (to a certain degree--which signals to you that they've outgrown their current plan), in fact you want them to, but not to the point where you take a loss. If they're seeing the value in the service enough to push the limits of their plan then they just need some time to internalize that value. You can then approach them about upgrading to a better fit package. You can also provide what are considered 'demand drivers' for 'free'. These are features that increases the value of the original service and actually drive increased demand as well.