I would never attend ANY simcha to which I am invited, for a few minutes and then leave.If someone thinks enough of me to invite me to stay for a meal, I think enough of them to want to be mesameach with them.
What I really detest (and forgive me in advance if any of you is guilty of issuing this type of invitation, but I think it is really rude), is getting invited to a shmorg and then to the “simchas chosson v’kallah,” which is specified for around 10 PM on a 5 or 6PM kabbolas panim. Does anyone really think it is polite to invite someone to get dressed for a simcha, come all the way down for the K”P and chuppah, then GO HOME (not invited to dinner, obviously) and RETURN HOURS LATER to dance the second round of dancing??????????? If you want to argue that the families cannot necessarily afford to include everyone, then make a SMALLER wedding of people you really want there, or do without some of the expensive trappings (a one man band can be fine, fake flowers can be fine to rent for tzedaka (I prefer to do that), and make a simpler menu and cake and fruit instead of a shmorg. But PLEASE don’t make some of your guests feel like they are on the “B” list. And also, if the baal simcha thought enough of you to invite you to the whole thing a) send back the reply card ASAP and b) show up if you said you were coming (unless there is a great emergency, and you should call the hosts as soon as you can to tell them). I cannot tell you how many seating cards I have seen left on the table that clearly were not even looked at, much less taken by the proper guest. The host still has to pay for you. It feels like gneivas daas to me to say you are coming and then be a no-show.
OK, done with my rant. For now.