Re: techniquies in street fights
Shomenuchi contains fundamental elemements of a type of attack (i.e. straightforward, commited and targeted at the head). Like many of the stylized attacks in Aikido, I think we train in it to become familiar with how react to that type of attack rather than one specific attack.
Ikkyo is an effective technique, but it also contains elements of defense that can be used seperately from the actual technique (i.e. entering strong, cutting with the hands rather than grabbing, and proper maai and timing).
I think Aikido is unique because of its levels of complexity, versus straightforward attack and defense techniques. It teaches us, through method repetition, to be better people, both in our self defense, and in our personalities. By learning to be brave in the face of danger and adversity and seeing an attack as an opportunity for action (things I've been told Ikkyo teaches) you might never even have to get in a streetfight, and that's more important that winning one, I think.