WishingH, if a woman is already receiving pleasure from what she has at home, there's no guarantees that bigger is going to give her more pleasure. Are you capable of sexually satisfying her? If she begins losing interest in sex with you, or if your sexual activities with her suddenly drops off, inviting a 3rd person, or even a couple, can quickly re-stimulate each of your sex drives. I believe both you and her will know when that time comes.
You might ask yourself the question ... "who, honestly, are you wanting this for?", because I sense this is primarly to fulfill your own sexual need, not necessarily hers. It's ok to admit that to her, and to yourself, that getting your wife to screw other men will re-elevate your sexual stimulation for her, but be sure to be honest with yourself, first. She may oblige you just to satisfy your desire. If no other cock has ever been inside her, I'd think it only natural for her to eventually be curious as to what other cocks would feel like. She'll let you know when she's ready.
If you do decide to follow through, I do encourage the two of you to play together, however. Giving her the clearance to simply go out and fuck other men on her own is a dangerous thing in many ways.
Good luck ... Mac
ps ... she's a doll, by the way. If we were close, I wouldn't mind a couple swap.