What you are talking about is not meditation in the fuller sense but a clearing of mind. Mokuso (and yes it does mean meditation) is supposed to be really a matter of a few seconds.
Robert Coit (rcoit) wrote:
Although meditation is momentary before each practice session, the strength of the art is in a well-founded, composed mind. This is developed by deliberation and meditation.
I agree with Mark. The longer, sitting in sieza type, meditation is a separate activity. It may personally help your Aikido just like any cross-training but is not necessary.