I like this thread, and I wish there were many more folks who respond.
For us, swinging was almost all positive. (The single exception is that std we contracted from a "friend," i.e., not someone we hadn't known for a long time. I discussed that in the thread on the downside of swinging.) I opened up and became much more sexual, sensual, attentive, appreciative, etc.
For my wife, the fact that I changed so much was reward enough for her since she didn't really care if she had other partners or not. Oh, she enjoyed the flirting and romancing and attention that she got from a lot of guys, but the sex was hardly ever really terrific. She could have given it up any time.
For me, I loved the variety. I loved the taste and feel of other women. I loved the sense of creating a new bond of friendship with several women whom I still adore and/or sleep with. It is a little like poly, but without the other facets besides sex and companionship. Maybe it is open marriage. I'm not sure what the label should be.
After sleeping with another woman, I was always hot for my wife. There was never a hint of betrayal or jealousy. Our bond was strengthened by the swinging. In part, it was because she was so generous in allowing me to do what I wanted. It also demonstrated so clearly that we were so well suited to each other that no other person could threaten our marriage.
For a long time, our best friends were other swingers, and swinging activities were the main "recreational" focus of our lives when children and work allowed some free time.
It is impossible to overestimate how much good the swinging did for us.