I think Rectangle and Hodgman have pointed out the inherent problem with splines: that given the right endpoints, they can produce some really acute turns up to and including pivoting on a point.
Like I said, I want constant forward speed with only gradual turns. Think of the camera as having momentum in the direction it is facing and that the only forces that can be applied are centripetal (and those have a maximum magnitude). This way, the camera will never speed up or slow down but will change direction to match the desired end condition.
To make it explicit, I'll use Rectangle's example where the start and end cameras are at the same position but with opposite orientations. The solution I imagine would probably look like a car turning around in a cul de sac.