I'm always wondering if power management facilities in a virtual machine is necessary?
And I'm not sure if they still function in a virtual machine.
Strictly speaking, no you don't need
acpid in a virtual machine nor on a real system. But you should install
acpid in a VM as it typically handles the power button press which is simulated by the hypervisor if you shutdown a VM.
So for practically reasons, yes you should install acpid on a VM.
acpid doesn't really do power management
I would leave it. I believe ACPI does more than just power management. For example I believe there is a ACPI event that is sent in via the VM Host to the guests when you want them to shutdown or reboot.
Excerpt from Manual:KVM:
issue ACPI shut-down command to KVM guest, if guest does not support ACPI, command have no effect.
issue ACPI shut-down command to KVM guest, if guest does not support ACPI, command have no effect. After KVM guest is shut-downed it will be automatically started by host when shut down is complete.