It is amazing how often us jumpseaters are denied being able to speak with the crew.
I have had many problems in the past for a variety of carriers and when you ask to see the CA the answer has been no every single time.
It should almost (within reason) be your right to request to speak with the crew if the agent has time to inform them. If the agent has time they should at least inform the crew of your intentions and let the CA make the decision whether or not to speak to the jumpseater, not the agents decision.
Back in the Eastern days my grandfather used to tell me the stories of how HE owned the jumpseat, PERIOD and there were no questions asked....those days are many years behind us, or at least coming up on 9 years behind us.