But giving too little also sends bad message, unless you can't afford it and the newlywed couple know your financial situation. If I were not in a position to give what I think is appropriate in the first place, I would not go. This is my personal opinion.
On contrary to clubchick's experience, for my wedding, I know exactly what and how much each one gave, except for anonymous gifts. I didn't want to keep track but my parents insisted so that they would know how much to give to reciprocate, for their children's weddings. Mind you that most of attendees were my parents' friends.
From then on, we kept track every gifts given to us, so we somewhat know in the ballpark, what to give in the future. Now you know that in this context, gift cards are the worst gifts since the values are known right away, to the penny. But if you can cleverly choose exotic gifts that look expensive that can't be easily found through regular channels, you can easily get by. And that, my friends, is the Spoofeean's trick