There are a lot of ways that rank is both interesting and useful, as a phenomenon within the aikido world. There are a lot of ways that it gets in the way and can even be problematic.
One of the ways in which I've found it interesting is precisely in the way it brought me to wrestle with my own goals and aspirations and desires as I progressed in AiKiDo. I started out feeling strongly that rank didn't matter to me. I remember avoiding my 5th kyu test for a long time. At some point I realized that avoiding the test was a way of showing how much it mattered to me. Later, I had to wrestle with feling like I deserved rank that I hadn't yet received. These sorts of opportunities to question myself and look deeper into my own attitudes towards my art, my sensei, my place in the art have always been really helpful to me and to my AiKiDo. They are one of the most important things about rank to me.