Had spiking all day yesterday and as you noted it will happen with both machines idle.
I think I may have a solution (and it wasn't the printer)
I have now disabled multithreading in both VEP and Kontakt. Last night I worked for about 1 hour with no spikes so I'll see how the rig goes today.
This spiking thing is quite nasty and get's worse over time. There is also a strange thing that happens when you quit VEPro. After quitting VEPro (and according to the Activity Console VEPro HAS quit) one of the processors will spike to 100% and just hang there for ever until I restart the machine. You have to restart the machine because you cannot move the mouse anymore and you are basically locked out.
I'm worried that no one else has seen this behavior. I'm starting to think that I have a faulty Mac.
I'll know more after today's work.