At the moment it is only possible to add build plans to one or more agents.

I would be nice it is possible to priorize the agents a build plan is running on.
For Example:

Plan1 is configured to run on Agent1 with high priority and on Agent2 with low priority.
This should mean that whenever Plan1 will be executed, Bamboo checks if the Agent with the highest priority is available. If this is so than the build will start on this Agent. If this is not than Bamboo should go down the next lower priority agent to run on.