It is quite possible that the benefits you mention would be lost on me, yes. I was in a monogamous relationship for a long time, but I still spend most of my time alone (not at work, either, I didn't have a job for most of that time, and my partner's schedule was such that he mostly spent night at work - sleeping - and so his days were spent at home too).
I guess I feel that when you spend too much time with someone, you benefit less from it (you're just hanging out at best, getting in each other's way at worst) and there is learn to learn about them, as they can't really tell you about their day if you were there the whole time.
I like spending time with my partners, but I like spending time alone so that I have things to share with my partners once I'm with them. I think that going to a movie as your date is a bit of a waste of time, as you're not interacting at all, and you could have seen the movie on your own and gotten the same out of it. When I watch a movie, or I read, I like doing it on my own, and then talking with my partners about it if they have done the same, or friends who have.
I guess TV is a bit different because you can talk about it as you watch without it bothering people. Still, I think you get less out of the experience because you miss what is going on due to talking over it. When I watch a show or movie on TV with my partner, I always end up having to catch it on my own so I can see what I missed.
I think some activities that get people closer can work with more than one partner. Videogames, board games, card games and sports come to mind. Basically, games. Actually, many require more than two players, and therefore are better with more than one partner.
I have noticed from talking with partners on skype (I've been in a few long-distance or partially long-distance relationships) that there is such a thing as spending too much time together. At some point you just have nothing to talk about, and being together just takes away from other things you could be doing that would enrich you - taking a class, reading a book, working on a project.
I do like working on projects together when it applies, though. For instance building a desk or a bed.
I guess in the end it comes down to the fact that after being around people all day (or one person for a long time), I need to be alone to recharge my batteries, relax, and get ready to face more people again. But when it's about being with the same person for too long, being with someone else fills that same needs, and so going back and forth between two partners rather than back and forth between one partner and being alone would help me deal with the stress as well. I would probably need a small amount of time alone every day, but definitely not as much, and I would see both partners as much as I would see a single one, as far as quality time is concerned.
It's probably simply that we work differently. My analogies were not meant to go around the issue, I find that I can discuss things better with analogies, trying to see if such and such situation would be the same or not, hence my suggestions.
I guess everyone balances between feeling crowded and feeling lonely differently. Some people could spend days or months without interacting with another soul and be fine, others could spend that amount of time without being alone for a second and be fine. I'm somewhere in the middle but definitely closer to the former.