I also need to make costume decisions too! Good point on Joann. I am reusing costumes for the 5k and 10 Miler. Thought I'd do Kevin for the 10K but seems like there are a lot of those already.
I struggle every race with getting "too clever" but ultimately you just have to decide if the costume is for you or for everyone else. I've put tons of effort into costumes that just one or two people seemed to get, but lots of comments on what I thought were lazy choices. So it's all about what you want to get out of it -- satisfaction or recognition.