Any flavor of the comment "I would happily pay more than <current price> for <what I claim I want>" is always hysterical to me. This kind of statement does two things that are incredibly naive:
First it suggests that you as the consumer know at this point what you would or would not pay. You only know what that figure is when it comes time to pay. If Amazon upped the price to $99/year and switched to private carrier and gave you no choice, you might not be so happy.
Second, even if you do know 100% that you'd happily pay more, it suggests that you as one data point know more about how to price a service like Prime than the legions of pricing analysts and product managers employed at Amazon who are privy to years of customer behavior data.
There's a reason Comcast and Verizon are constantly bitched about by consumers yet continue to lead their industries in customer volume. Individual consumers are fickle but really only care about immediate cost.