This type of thing has come up before, but anyway, I like to see myself write:
I've done a bit of Judo and Karate (and Tang Soo do), and although they were quite enlightening, I found they restricted my approach to self-defence (mainly due to lacking the concept that someone could do something different from outside their own particular style). The differences between many martial arts aren't techniques, it is emphasis and training style. In aikido we sacrifice one type of realism (through comeptition) to gain in another (we are aware of more things the attacker could do, and examine body movement principles).
As a responsbile aikidoka, it is important to understand other martial artists and what they can do, but not necessarily to train in the same way.
Main conditioning execises:
simple bokken cutting
basic atemis for common aikido techniques
catching bricks with fingers (strength for pressure-point striking)
All these benefit my aikido