We have MiCd running in the lab and have put the manager and media on one server only to reduce cost in the lab environment. Also, you only need one Media server to one Manager server. So if you have 50 MCD instances on the Manager, then you will need at least 50 instances on the media server.
Also, this is a Mitel virtual platform for MCD. So, when you compare to VMWare, you have to spend a bit of money to reap the benefits in the long run. So a ROI would be when you have more than 6 instances.
I hope this helps.