I think atemi is vital for any true self defense situation. It is not necessary to crush your opponent with a devistating atemi, but I feel that it is important to misdirect or trap their attention with an atemi. I believe this allows you to finish the rest of your technique 100% effectively. In a true self defense situtation 100% effectiveness can be a matter of life and death. If you are fully confident in your techniques and their effectiveness then perhaps you do not need any atemi. This would be the most harmonious and loving way to defend yourself, but I believe this confidence takes many many years to achive.
Personally I just try to stay out of any situations where violence can occur, or at least try to change a situation of tension to one of relaxation through the use of the right words.
In daily akido training I don't think atemi are as important but the techniques should be learned nun the less.