Wow, we have been out of the loop for weddings around here, waiting for the grands to get old enough and all our friends kids are already married.
I was shocked to think that any one would expect to "cover a plate"! Why not just save the money and not invite some one you don't really want at the wedding just to get the "Gift" and if I was paying for a wedding then I would never expect my guest to "cover a plate"! In fact I wouldn't care if there were no gifts, you would have been invited because you meant something to the family and your being there to celebrate would have been enough.!
Sad when people only think about what they can get or feel entitled to!
I would give a check instead of a gift card, and any amount you care to give should be appreciated.