She wants you to go to the memorial because it's an annual show. If you really want to see the crazy in action, you need to go to a regular Sunday meeting and a regular weeknight meeting. The memorial won't give you a true idea of what being a JW is about.
My advice is to go to a regular Sunday and a regular week night meeting to get a true picture of them. Going to the memorial might earn her brownie points, but if you really want to learn about what goes on there on a regular basis, don't waste your time.
You don't need to wear a suit, but khakis and a button down shirt would be good.
Also, I dont agree that you want to go late so no one has a chance to talk to you. I would think you would want to meet, even if only superficially, the elders, especially the ones that had a private meeting with your wife about her sex life! Get a feel for those men. ( Optional to tell them if they ever talk to your wife about her sex life without you again, you'll knock their teeth out. ) Do people not get how inappropriate this is?
Set out boundaries in the beginning with your wife. Two meetings and that's it, just for your own personal information. Do not go to more meetings than that. Their intention is to convert you, no matter what they claim.
Oh, and that "really nice guy" that came up to talk to you? Yeah, it's all a show. He's probably not that nice in real life. He just wants the conversion brownie points. They are fake, fake, fake with outsiders. But, you'll get more of a feel about how they really are at regular meetings than at the memorial. The most frazy will be showing at a midweek evening meeting.