I have video taped this genre' for 8 years. I do interview the guest at the reception. I like to wait till they have some liquid courage in them. Just two weeks ago I started to ask the people more about them first, then asked them last any well wishes and marriage advice. This approach seemed to deliver more deeper messages. Don't get me wrong I love a drunken idiot on camera it gives us a lot of comedy time once we are in post.
I shoot that a lot, but what I do is grab either the best man (or chief bridesmaid/matron of honour, or the MC) and go around with the mic and get them to ask the people. They get more out of them that way, otherwise it is too difficult to work the camera and the people at the same time.