If you don't want to do gift cards, don't. A gift is a gift, give what you want or don't bother to go. I think the invitation could have stated 'gift cards suggested but not required'. or something similar and not tacky. Some people like the ease of purchasing a gift card, others want to chose something more personal and delight in the search for the right gift.
I also find the trend of having party guests make out their own thank you card envelopes with name address to be extremely tacky and on the edge of rude. We spend our hard earned money to purchase a gift, spend time and energy and then asked to make out the thank-you envelope? The recipient should take the time, energy to express sincere thanks and make out the envelopes and send the thank you card. IMHO