Hi Brian,
It sounds to me like you and your wife have been together for so long that you want to stay together still, mostly out of convenience and to avoid the hassle of divorce. Being that I am waiting for my divorce to be finalized by the courts (any day now!), after nearly five years of separation, I can understand wanting to avoid that drama - though sometimes divorcing is the better solution, even after so many years of marriage. I know someone whose parents divorced after 40 years of marriage and they both could not be more happy about that decision.
Though there seems to be respect and caring in your marriage, there doesn't appear to be much compatibility anymore, nor sexual desire or affection, from what you've written. I think it is a good and thoughtful question to ask yourself, "What joy and happiness would I be able to bring to a relationship with someone new?" BUT the part you wrote about seeing yourself as "unable to provide" that in your current relationship may be a bit too harsh a judgment on yourself. You and your wife got to the state you are in together, so I hope you are not solely blaming yourself. Each of you are 100% responsible for your parts in how the marriage has gone.
I mention this not only because your words struck me as a bit hard on yourself, but also to point out that if you do become romantically involved with someone else, whoever that new person is will bring her personality, relationship skills, history, etc. to the relationship and together you two would be creating your own dynamic. It would not be the same dynamic you have with your wife because you would be with a different person (and I highly doubt you would pick someone similar to your wife since you have a certain level of dissatisfaction with your incompatibility). So do not think it will go the same lackluster route, though you would probably do well to look out for any patterns of behavior in yourself that might steer it that way. You also might find that your "equipment" will start working again,or more often, with a different partner -- and there is always Cialis, Viagra, or Levitra (though I know sex is not your focus in seeking a new partner).
But that is putting the cart before the horse right now. You're not there yet. I think polyamory could work for you, because your questions are thoughtful and you seem to want to be considerate of your wife rather than cheat on her. That is great.
As far as polyamory goes, don't get caught up in thinking of it as a "thing" you need to handle. What I mean is - look, the terminology is fairly new (in use since the 1990s), but the concept isn't. My own great-grandmother had her boyfriend living with her and her husband when they were in their 70s, back in the 1960s. There have been countless married couples throughout the ages who have had an "understanding" that allowed one or both of them to roam. However, many polyamorists today feel that poly is a political movement, others dream up long lists of rules to follow, others come from swinging and think that it should work like swinging does (it doesn't, really), and there is an awful lot of jargon and theories that get tossed about. You don't need any of that.
You never even need to use the word polyamory when talking to your wife or trying to meet someone new. You can tell your wife that you want the kind of closeness and companionship that you know she is not interested in providing for you, so you are asking for her blessing in having a girlfriend. It's really that simple. And then you would be just as honest with any potential girlfriends and tell them your wife approves of your having a girlfriend. If you are honest, respectful, kind, and considerate, I don't know how you can fail.
