Thank you for your response. After reading my initial post again with a critical view, I see how one could come to another interpretation than I intended. But it seems to be worked out now 
To answer your counter-question:
1. If one machine sees a unit as barely used, the other should too. If a unit is good for, say, 50k copies on one machine, then it should also be good for 50k copies on another, not 0.
2. Keep in mind that these particular models are pretty old and that they usually don't have service contracts on them anymore. Basically, any extra life you can get out of them is a bonus.
We started on one of these old machines, but as time went on and our business grew, we decided we wanted more reliability and predictability (fixed price per page). That's why we invested in a new machine (2009 model) with a service contract that includes consumables.

To answer your counter-question:
1. If one machine sees a unit as barely used, the other should too. If a unit is good for, say, 50k copies on one machine, then it should also be good for 50k copies on another, not 0.
2. Keep in mind that these particular models are pretty old and that they usually don't have service contracts on them anymore. Basically, any extra life you can get out of them is a bonus.
We started on one of these old machines, but as time went on and our business grew, we decided we wanted more reliability and predictability (fixed price per page). That's why we invested in a new machine (2009 model) with a service contract that includes consumables.
Comment