Stuart also asked . . .
1. Production management theory (throughput theory) requires that the 'bottle neck' feed has a higher capacity then the 'bottle neck' to maximise the throughput - can one use this spare capacity and at what rate should it be costed? [Clearly any 'non production line' work taken on by these 'multi skilled', 'non-multi tasking' resources carries priority 2 and must be dropped when the 'production line' demands their attention.]
I'm not really clear on the idea on costing spare capacity. In any multi-project organization, there is beaucoups spare capacity and the allocation of specific costs to specific throughput events is a common source of bad decisions. Therefore I'm having trouble with the question.
Of course the "spare capacity" can be used for other purposes. Buffer management and relay-runner work practices guide them on the best use of their time and attention at any point in time.
I probably need a bit more clarity on the question you are asking.