I think Dave gave an excellent view on the relative merits/drawbacks of muscle power in aikido, thanks.
I see aikido as a mind/body/spirit art that seems to have (on these fora at least ) a slightly unbalanced bias towards discussing the body, at the expense of the other two, particularly the mind. For me the 'mind/ki' in aikido is every bit as important as the body. Our bodies are useful as they are transport mechanisms for the mind, they get us to where we want to go.
Early on in my aikido practice I was asked by my teacher of my training partner "How much does his mind weigh?" "nothing i guess" was my obvious reply, "So you don't need any effort to throw him then. The mind leads the body, if you can lead his mind his body will inevitably follow, it has no choice". I struggled with this concept at first, but now it has become the central part of my exploration of aikido. No amount of physical strength is going to overcome something that isn't there, strength needs something to push against.
For me the closest I can come to describing what this feels like in action is - when you go to lean against a door and at that precise moment someone opens the door from the other side, or - you are running up a flight of stairs and you go to stand on a step that isn't there. In both cases your mind expects to feel something and it doesn't get what it expects. This is where I believe the 'power' lies in aikido. When nage knows uke's mind and respects it fully, he can enter into aiki with their mind as well as their body. This for me is where the beauty of aikido resides. Effortless technique is fantastic for both uke and nage, it is the real enjoyment of the practice for me.
So big or small, well muscled or not, my desire is to perform every technique with the absolute minimum of effort. It doesn't always work for me of course, and when I come up against a physically strong training partner and I revert to using strength, I am quickly aware that If I continue in that vein, I'll get nowhere, so I keep practicing the principles.
So training the body, nothing wrong with that, go for it, although I think flexibility is just as important as strength training, if not more so.
Training the mind is essential to progress in aikido, how can you hope to control someone elses if you can't control your own?
Then there's the Spirit.... now there's another whole thread entirely...
just my 2 penneth worth