I think the combo is fine. It's a bit conservative, but it does match. Anyway, if you want to liven it up, go with a brown or burgundy tie, both colors pair well with blue. I'm not a fan of the black knit tie.
I'm going to a friends wedding tomorrow and was thinking of wearing a dark blue three piece suit. It's a semi-formal event, but not black tie. Most of the guest will be wearing conservative suits. Do you think a three piece suit is too much? Does it attract too much attention?
It's totally fine if it is a solid Navy or even a solid Gray suit jacket. Some patterns may be okay too, if they are sporcoat-like patterns, but I'd stay away from striped suit jacket and the like. I know some will disagree with me, but what difference is there between a solid Navy blazer or suit jacket?
I agree. Black is a definitely a no-no for a wedding. While Navy is acceptable, it just doesn't have that light and fun wedding feel. I would go with a burgundy tie as suggested previously or any other more colorful contrast color.