It's easy it is to pull together bits of all sorts of things, attach them here + there without a plan and make mail art!
Two things are pushing this burst of mail art. First, of course, Hanna's swap! And second, I've been reading Good Mail Day: A Primer for Making Eye-Popping Postal Art. Mail art is such a pure and wonderful art form. It is made to give away, sent off to points far and near and appears in a friend's mail box through the magic of the postal service. I think it would be easy to utilize the ideas from this book to transform your art journal into something very wild and free. Get your mind off the end result and just start putting stuff out there.