Introducing a new budgie to the flock?

[zaza]

I currently have two little budgies, Bonnie and Clyde ( http://www.youtube.com/watch?v=T8pm5ZunpBA ). I've had them since April, and they were not hand raised or tame. However, they are still under a year old. Their cage is big enough for at least 2 more budgies to live comfortably and still have plenty of room to fly and scurry about. I'm not buying a new budgie anytime soon, however, in the future, I would like to know. These birds are only semi-tame, as you see in the video they are playful and are in very good feather. They will sit on my shoulder and with some coaxing the male will let me pet his tummy and his back. The female always starts a singing game with me where she'll get as close to me as possible (while she is in the cage) and she will chirp very loudly. She gives me a little look, then I whistle back at her. We can do this for hours! However, they still aren't completely comfortable with me, and like I said before, they are just semi-tame.

My question is, if I were to bring in a hand raised friendly budgie to the family, will the other budgies learn from his example? Would they only become more timid? Would the hand raised budgie start to become fearful of me? If I ever do get a new budgie, would it be easier just to have him in his own cage?

Thanks