obviously the more you train the better you get, but I think it depends very much on your personal skills and aptitude what you will get out of the training. In my dojo, we have four classes per week, and most aikidoka come only twice. Myself and two or three others come four times, and I don't see really a difference in our advancement; apparently we just need to put in more effort to achieve the same.
Or maybe there's just a point of diminishing returns. I think that's true in general, whether or not it applies in your case specifically.