That poll is a little bit bias, because Plus has great features (I usually work around them, but wished more than once we had bought the Plus license!). But the question mention performance boost, which is the least reason I would consider the upgrade. Is NGNX your performance bottleneck? If so, either your service probably don't do much (no critic there, just to mention the processing of the services behind nginx is super low), or there's some misconfiguration - like costly regex - in your nginx setup, or some architectural problem. In short, Plus has some great feature, but if the reason to upgrade is to get a performance boost, I would step back and analyze my stack to understand where are the current performance costs.

I didn't think Plus offered any performance boosts over the free license; that would be a pretty poor business strategy I think.

That being said, what exactly does the Plus license offer over the free license aside from support? What are the feature differences? Are there important directives available through Plus that are not available through free, which would make certain setups impossible?

I'm new to this whole server administration / setup thing, and have been wondering this recently as I try to set up a server.

usually nginx is not the bottleneck of the application it's more common that it's PHP.

The question is if a good configured varnished / cloudflare or other cache / reverse proxy wouldn't get the same result.

But all those things are hard to tell there are a multitude of factors to consider in the architecture alone :)