Re: HOW does aikido change us?
To simplify things a bit, let's assume that all the changes any individual experiences go one way or the other, even though we know this is probably not true.
That said, I believe the basic change mechanism in all of the activities that have been cited is continual repetition of behaviors (physical, mental, spiritual, etc.).
For folks who have changed for the better, the behaviors have been those that society might consider positive or valuable. For those who have changed for the worse, the behaviors have been those that society might consider negative or troublesome.
This repetition of behaviors is reinforced (possibly rewarded, but at least tolerated) by the reactions of formal and informal leaders in the community of interest (i.e., the dojo).