Should I Send Thank You Cards to Everyone Who Attended Our Wedding or Just Those Who Gave Us Gifts?

I'm a little confused about proper thank you card etiquette in this situation. There were a couple people who attended our wedding who did not give us a gift..do I still write them a thank you?

Suggestion:

Everyone who gave a gift – absolutely

Everyone who came – the etiquette is murky on this. To me, since it's only a couple of people and they at least took the time to come to the wedding, I would send a thank you note. A kind gesture is always appreciated, and it makes you look super classy.