Peter,
Didn't morihei once say that he didn't truly understand/appreciate aikido till he lost his strength? I can't remember but I heard about something to that degree in my readings.
In my very limited experiance, I have found that even the most out of shape people can be really great aikidoka. The only thing my personal physical abilities have really helped is with the knowledge that I could run away from them if we ever got into a fight
I am not saying there are no advantages to lifting and being in shape. but to quote a sempai. "hmm... your in shape. thats nice. not needed, but nice"