Thank you for your response, need to pelt you with question now though so brace yourself! 
If I did an expandable reservation, wouldn't that prevent vSphere from taking resources back from a RP in the event that other RPs start to consume more and need their reservations back? Would there even be resources that the expandable reservation could claim if I have already divvied up 100% of my cluster resources evenly as reservations across the RPs?
And sorry, I should have said that RP reservations do not behave exactly like VM reservations. I thought that they would not prevent VM's from powering on since the VM itself does not have a reservation. Just that the VMs inside a RP would be guranteed the resources inside the pool and if for example the cluster was at 100% usage and every RP was using it's maximum amount of reservations, the VM's inside a RP would fight for resources the same way they would if they were in their own cluster with no resource pools?