Cloud economics are most sensitive to VM density and less to automated virtual infrastructure management. If the VM density decreases as self-service portals are introduced or SLAs enforced, it will undermine the cloud economics.
The way to increase the VM density is to offload functionality from the VM that creates headroom or "idleness" in CPU, memory and IO. Creating virtual versions of network services as VAs is exactly what you don't want. Having a footprint on the virtual server backed up with HW acceleration outside the VI is what will increase the density. In other words, virtualization of network services is not a P2V activity but more a distributed computing exercise