I know its not a good idea to share everything (information) about yourself with a women, even if you know each other well and for quite a long.

Who say's it is not a good idea?

How can you be sure that that was the reason? or was it a speculated assumption from your part?

I'm not sure but definitely it contributed.

Intuition tells me that telling everything about yourself makes you less valuable.

Lets face it. If I tell you everything for my self from the get go how valuable I'll appear to you?

How would you feel toward some one that says - you are well come, here is everything that I have, do what ever you want with it, I let you all my control with my all permission.

When in such situation people usually take advantage.

Come on you know its like that, no point to explain about this.

You have a point on 1st dates. but to a girl you're in a relationship with, you pretty much know everything, it's like you're still gaming these girls or something.

I never tell girls about PUA, but I have told some I used to be shy and I am into self help,

but, i don't stay mysterious as a tactic on the girls i have a bit of an emotional thing going on with.

1)Never EVER talk about your exes. It is the first thing someone will try to use to hurt you on any argument and on a break up. Don't even mention things you were doing with your ex. Any information about your past relationship could be used as a "manual" on how you are going to react.
Even if you share good things about your past relationships... for example you treated the ex to a fancy restaurant. Your current gf would expect you to take her to a fancy restaurant too and if you won't then she will tell you that you are not taking your relationship seriously.
2)Avoid talking about extra bonuses that you got from work unless you have the intention to spend them with her. If you worked overtime and the company rewarded you with a trip to Paris, tell her, take her with you have fun etc. If you got a bonus that you want to save up don't say a thing. Even if you are married. You might feel excited but go and share your happiness with your mum and not your gf. If your gf knows that you got 1000 pounds and you spent on her only 5 pounds for a burger or as some PUAs here would insist on not spending ANY money out of that bonus with her... she will start not liking you.. because you are not taking her seriously and not investing in the relationship. Even the less materialistic women will talk about this behind your back with their female friends.
So keep your mouth shut about your finances as much as you can. She might not have the power to do much about it but to keep your mind at peace and your life drama free... better forget to mention this.
If you can also keep private the information on how much you make each month that's even better.
3) avoid talking about your family matters. Your gf doesn't need to know about auntie A that had an argument with auntie B .. or any other members of your family. If she is not your wife and the situation doesn't affect her this type of gossip is better kept for your close family
4) Don't share about any embarrassing experiences you had unless you are ok to be picked on them. You might need to show some vulnerability and talk about that day that you did something silly and it's ok but make sure that it is something not that serious and you are ok to be picked on in a case of an argument and it won't be bad for your reputation if she starts talking about it behind your back.
Some things should be kept secret
5) Don't share the story about another woman that you fell in love with in the past.
6) don't tell her about your mates' secrets... or bad gossips or even talk often badly about your friends to your gf. If you argue she might want to take revenge on you and go and tell them. Sometimes this might not be possible but keep it to a minimum if you can.
7) never mention about the number of women that you slept with. If it is low she might think you are inexperienced... if it is high she will think you are a manwhore and not be able to trust you. Don't ask numbers and don't tell numbers.
If you want to brag about the girls you slept with do it with your mates at the pub when it is only men listening.
I had someone once tell me that he slept with over 250 women.. I couldn't trust him. He either couldn't control himself or he had just lied to me. In either case he wasn't trustworthy..

Maria, honey, how is your marriage goin'?

Lowdarlin', how much you reveal depends on what kind of relationship you are having.

I assure you, every information for the list you leave out will come back and bite you in the ass.