I don't use any other mathematical/friendship/family theories for gifting other than what is in my bank account and if Cousin Joe gets mad because he only received $100 from me and I should have given more because I am family or he sees I have a job or whatever misplaced idea he has, then he is welcome to give it back to me. I am a single mother raising 2 girls on my own and if someone thinks that by inviting me, I had better be covering my plate so they can pay for their reception that I had no input in, then by all means, do not invite me. Unfortunately, the wedding business has gotten out of hand in convincing brides they have to have the biggest and most expensive of everything and then these SS's are let down when life smacks them in the face because their guests actually have their own financial things to take care of and are not able to cough up $400 for a wedding gift. I know very very few people who ever received more than $200 from a gifter at a wedding, and it was usually a parent or grandparent that gave that. Whatever a person is able to give, the receiver should be grateful to get. If you want a money making venture, have a carnival..have rides, a petting zoo, snacks, games and sell tickets.
The last few days I have asked some friends about the cover your plate idea, and most just laughed. My step brother, who was married a few years ago said the thought of asking his friends and family to make sure to cover their food and drink was laughable. He said they were thrilled to throw the party and have their nearest and dearest there that it didn't matter what people gave..or in the case of Step sister and her hubby and son (who was not invited) didn't..that didn't matter to them as long as everyone ate, drink and was merry. That is how to throw a reception!