With regard to sparring, it is very difficult to apply what you know to a situation where the other person has a completely different aim to you. I used to be very interested in how I would compare to a practitioner of a different art, but really aikido is not suited to a situation were somebody is try to pick you off or tap you on your nose. Plus a karate person (for example) will never commit an attack or close in when they see you aim to enter and apply technique. This can be very disheartening and probably best avoided.
With regard to this idea that you would never get a clean technique in randori, I have several quicktime videos to show this is not the case. Is there a place I can upload them to for people to see?