Best route to move from Essentials Plus to vSphere Standard?

I currently have three licenses for the Essentials Plus kit of vSphere 5.5

In order to add storage vMotion, I will need to move to vSphere Standard.

It is my understanding that the vCenter Server from the Essentials kit differs from vCenter Server Standard, so in order to move all my existing environment to vSphere Standard, I will need to purchase vCenter Server Standard and 18 CPU licenses for vSphere Standard.

Is there an upgrade path for the move to vCenter Server Standard or are customers essentially forced to start from scratch?

If there is an upgrade path, does pricing differ than starting from scratch?

There was a post in early February about moving from Essentials to Standard, but in that particular case, the organization already had vCenter Server Standard, so all that was needed was the CPU licenses.