Hotkey (or other quick way) to insert a keyframe for only one component of a vector-valued property? I want to keyframe only the x-value of the rotation while the y and z are being animated independently. (If you want to know why, I'm making the camera continuously revolve about the z-axis at the center of the scene and using the x rotation to change the polar angle at one part.)

I can achieve the effect using the dope sheet to delete the y and z keyframes after I use the I hotkey to create a keyframe for all three values, which is honestly not so bad, but it seems like there should be a Ctrl + I or some other way to have more fine control of keyframes without having to open the dope sheet.
One of those times when you discover the answer right after asking. Hopefully this helps others.

You just need to right-click the single value you want to add a keyframe to and select "Insert Single Keyframe".