You need to consider both average utilization and peak utilization to do this properly. I’ve found most Windows stats don’t really give you all that you need so sometimes it will be a gut feel.
Not a full answer but something to make sure you remember.
Once you get your stats and feel for what you need to do, discuss with the user/sys admin for that system. They will be able to tell you far more details about the usage pattern, the likelyhood of customer buy-in to virtualization, etc. And, you would make them feel part of the decision.