Also, why are you limiting yourself to "single women?" Why not date others who are married, like yourself? And, how long is it before you reveal that you are married? Were they meeting you in scenarios where a mono mindset is the defacto expectation?
This is what I'm thinking must be going on. As I said to another poster in a similar situation recently, you need to not bother investing time and energy looking for bread in the hardware store. Go to the bakery. The bakery is where the women who are already open to polyamory live. The hardware store is where women who've never even heard of polyamory live. There might be more women in the hardware store, but you don't want a monkey wrench, you want bread.
To address your main concern: I understand that dealing with this kind of envy is really hard. I've actually been there myself because my girlfriend is all kinds of hot, and is really good at connecting with people, in a way that isn't quite as easy for me to do. We are different people, so it stands to reason that one of the things that is different for us is how we attract other partners. The thing I realised early on though was that if I expected to do things the same way she does, or expect to have the same kinds of relationships in my life that she attracts, with her energy and way of seeing the world, then I'd be setting myself up for a mother load of pain. I think one of the most painful feelings I've had to deal with in the whole opening up process has been feeling envious and insecure in myself because of comparisons I'd been making between myself and my partner - my partner who I love so dearly, who loves me so completely. It's such a fucked up situation to be in, and I can understand wanting to slam the lid on that, I really can. But I think, as others do, that it's a matter of riding that storm out.
Even if you met a woman tomorrow who wanted to date you, it wouldn't even things up with your wife. After all, she's had a lot of interest. Probably has some relationships of her own that are more developed. This budding romance with this new woman in your life might fizzle out just because you are not so compatible - nothing to do with your status as a married man. That's just life. That's dating. It's never going to be 'even', even if you guys go back to sharing lovers. Even if you guys go back to monogamy. Because if you do close the door on her having other relationships, then what she is giving up is something more than what you are giving up - and that's unfair. Sorry. But thems the breaks. She might be willing to do that, because it sounds like you guys are close, but make no mistake about it - you are asking her to live with something as unfair as the situation you currently perceive. (And I agree with HappilyFallenAngel here: this really is about perception. So much of the pain you are feeling is self-generated. I know, because I did it to myself too).
So what to do about it? You are clearly unhappy, and I do think it's important that all parties 'get something out of poly' as you put it. It doesn't sound like you have an issue with polyamory in itself though. You say you don't get jealous, you feel happy that your wife is happy. The issue is that YOU WANT TO DATE OTHER PEOPLE, and you are not having any success in it. So therefore the solution is to GET BETTER AT DATING OTHER PEOPLE, not to quit polyamory (unilaterally, for the both of you) altogether. I think that's the logical disconnect that people on this thread are bumping up against here. Your proposed solution to icky feelings does not address those icky feelings in any reasonable way.
I get that there could be a cycle at work here though. Perhaps your lack of success in the face of your wife's success is hitting your self-esteem and ego pretty hard right now, and then that perpetuates into your behaviour when you meet new women. Maybe you come across as pushy or desperate, too keen to 'have what she has' immediately without realising the slow build-up that's required, or even not caring that much if you and the woman you are talking to are even that compatible, just wanting to get laid so things are 'fair' (word to the wise: women can smell that shit a mile off - it stinks).
Perhaps I am being overly harsh, and you really have just been unlucky about meeting good people you connect with though. And perhaps your wife, as wonderful as the picture you paint of her is, has been neglecting your relationship a bit in favour of others. I don't think it's unreasonable to ask her to slow down in her conquests - maybe even take a break from finding new partners for a while, and invest a bit more time and energy into your marriage. Perhaps that will provide you with a bit of a mental break and allow you to regain your confidence a little, and get a grip on feeling competitive about dating in your own time, enough for you to feel more like poly isn't taking anything away from you. Of course, at the end of the day, if you have already made your mind up that the only solution for you is to close your relationship then fair play to you. You have every right to decide what kind of relationship structure you want to participate in. Just remember that your wife has the same right, and that even if she decides you are more important than having the freedom to pursue others, that's also a sub-optimal solution (for her and her current lovers at least).
If it were me, I'd be leaning toward the more courageous option that has me dealing with my own insecurities without placing restrictions on others (or walking away if I truly knew I couldn't deal). Envy is an ugly emotion - we don't like looking it in the eye because it forces us to acknowledge things about ourselves that are unpleasant. However, once you do and get to grips with it, you don't have to do it ever again. I'd add that firmly in the bucket of 'benefits of an open relationship'.