Before I left Aikido, I studied the art for more than 10 years. I was really hooked on it, practicing 5 days a week, 2 classes a day for months at a stretch. Suffice to say, it was a healthy addiction. I got to Shodan (under the Aikikai) and I didn't see the point of working toward a higher rank. I was practicing the same material as my seniors and I could spend the rest of my aikido life working on my skills at my present rank.
It seems to me that you have reached your goal as far as what you wanted out of Aikido. . Unless you want to teach what you have learned, with your unique perspective, to others than it is time to quit. Nothing wrong with that.