Nufutz, what these fine ladies - and men (you beat me to this Spoo!) have said is some wise advice and I would only offer up a presumptuous question: what does your wife understand swinging to be?
Many people have misconceptions about swinging. Read a bit here, bookmark some threads you like and if you still want to pursue it, ask her to keep an open mind, then show her what you've found.
To me it's one thing to understand a thing and reject it, but quite another to reject it without awareness.
Welcome to the board!
-B