I just got married this summer, and I really enjoy discussing etiquette.
As far as wedding gifts go - It's technically not very cool to tell people *what* gifts you want, since that's implying that you think they intend to give gifts (which are actually entirely optional), but I don't think etiquette should ever get in the way of common sense - a registry for the household items you want, linked on your wedding website, for instance, makes lots of sense. (This way those who want to use a registry have easy access, and everyone else doesn't need to see it.) My husband and I live in a city, don't have a ton of space in our apartment, and I really don't like clutter - for that reason, we just didn't register anywhere or say anything about gifts. Then, if anyone asked about registries, just politely said we weren't registered because we have limited space. We got a mix of gifts - some of our guests gave us their presence, others brought cards with messages, most with checks or cash. Some people got us physical gifts. We mailed our thank you notes within the week and appreciate everyone's generosity.
The notion that you 'should give enough to cover your plate' is abso-fucking-lutely ridiculous. The number one rule about giving a gift, is that you give what you can afford. If that is a card with your well-wishes to the couple, that is entirely reasonable. On top of that, it's pretty much impossible to know how much a couple spent on their wedding, so you can't do this even if you wanted to. ;)