I think a "zippier" name would help to make it less somber -- the "Wall of ..." is a serious-sounding phrase. How about "The Grat Wall," playing off the "great wall" in China, which most have heard of, and the "Grat" makes it less formal sounding. Imagine telling someone, "Oh, your picture is up on the "Wall of Gratitude" versus on the "Grat Wall." You likely have better ideas for a name, but it's worth thinking about something people would refer to often, since that is the goal of the project! Good luck!