Outside of wanting many partners and restricting partners to one, are there really differences between these mindsets?
I think yes, there are. Though, maybe there's something more specific there, the idea of "defaults" create differences.
Mono (on this forum) doesn't call himself a polyamorist but he recognizes that love CAN exist between two or more people without limiting or negating the love that those same people can have with OTHER people.
So Mono doesn't see monogamy as a "default"; it's just not his thing.
There are some people who see monogamy as a default, and it (in my eyes) taints their relationships.
The whole "sex thing" is a very, very small part of the development I've undergone since becoming poly and LIVING poly. What has really been amazing is how I no longer feel restricted, not socially and not internally, for letting relationships being what they will be.
I've had 'crushes' again, and felt great talking about them. I'm feeling that amazing "falling in love" again and it's something I once thought I'd never experience or share again without a tragedy first.
But that bothers some of my mono friends. To them, sex and love are so tightly tied to the "default" of monogamy that my very presence threatens them, or more so, makes them face their own insecurities.
For instance, I have a hetero-mono couple that are friends of mine. And I trust the lady quite a bit and by extensions, I've discussed some things in their company that are more intimate than I'd mention elsewhere to just 'a couple of friends'.
One of those things was that I no longer consider my personal relationships "capped". People I love and trust don't have to be sidelined for fear of making my wife uncomfortable. I no longer have to toss that "I'm married" disclaimer in when I flirt, because it doesn't matter. If the relationship MIGHT "go there", it CAN go there and still be a-okay.
But shortly after that discussion, the male friend of that couple became a bit guarded. To him, the idea that I don't INSTINCTIVELY cap the possibility of my relationship makes him feel threatened. This is an issue, since he's feeling insecure and that's not a poly/mono thing, but the reason behind triggering his insecurity DOES fall into the area I would consider "a value difference" between monogamy and polyamory.