Re: Aikido as an alternative to judo kata?
I have simultaneously trained in Judo and Aikido. The 2 arts blend together very nicely and are complimentary, given that they essentially work on the same principles.
The "aiki" feeling you describe doing kata is what Judo is supposed to be. The "muscle" feeling is the difference between American Judo and Japanese Judo. The idea in American Judo is to pick your opponent up and throw him down. In Japanese Judo, the idea is to break his balance first.
Doing Aikido once a week will probably give you back some of what you miss about Judo kata. It may also help you put some of the Ju back into your Judo.