Ukemi are important. You must remember that Aikido is not so much a sport as a fighting art. Therefore, I believe that Ukemi are as important as other techniques. If your Ukemi become proficient then you will follow your partner better because the fear of falling will have gone. This will allow your mind to be calm and as the body always follows the mind in Aikido then it will be more relaxed, giving you more speed and natural movement for your technique.