Wow, this thread is actually really inspiring; I'm kidnapping a couple of these ideas (sending everyone a flag-decorated alpine panel, giving everyone a yard -- I toyed with the idea, but forgot about it for a while).... Speaking of that last one, my thoughts for giving villagers without much room directly in front/behind/to the side for a yard (I have one -- camp on one side, path on two, cliff on the 4th) is that I might give him a space just across the path for "his" garden, since I'd put a log bench for him to use. I may give another character in a similar fix a little secret fairy circle. Thanks for the ideas!
One thing I have done is give all my villager's houses a little lining of flowers/ores/etc, reflective of the characters. I need to finish these on the last few, but the idea's added some character, as I work on translating colors. Another thing I like to do is, when a villager visits my house, talk to them in every room of my house until they comment on something about how I've decorated it (A piece of furniture, that there's rare stuff, that it has everything, or something specific and variable like that). When in their rooms, I'll have an emote party with them, especially dancing and singing.