On not inviting the +1 unless basically married, I think that depends on the venue/other guests. I mean, can you imagine if you are the type who wants a date (or friend) with you so that you can have a nice time since most around you are in couples? I have gone along just as a friend to receptions several times years ago and it was kind of fun. Again, depends on the situation, but if you are throwing that big of a party are you really saving that much by not inviting a few +1's and also it may lessen the fun of the intended guest.
That fact that all of this is still going on in this era as people have posted about how many of us have had our own households prior to marrying and the 60+% divorce rate is crazy. I like the idea someone posted about a party after you have achieved so many years together.
Sorry for those of you left out or not invited to the wedding after participating in the gift/$ grab.