I was just on the phone with a friend of mine about 20 minutes ago. He was telling me about his wedding, which is coming up soon. He told me he's getting 'all dressed up' which consists of a black dress shirt and khaki pants. I was just kinda surprised that that's proper attire for a groom these days. I didn't say anything, because it's not my wedding. I would have been offended if people came to my wedding dressed like that.
Hate to say it, but the common etiquette seems to be do not dress better than the bride or the groom. So you might have to carefully consider just how well you want to dress, assuming you take that advice into account. Although I don't imagine you would be the only one in a tie at a wedding.