Yes I would agree that the lost of Buchannan was important. I would also agree that no enemy wants to engage their opposite number in a position of equal or lesser strenght. The fact that the CSS Virginia was not operational due to refitting her with a ram and extra armor allowed the Union Navy to change the balance of power in Hampton Roads.

I am also sure that the Confederates naval authorities did not want to risk the loss of the Virginia either engaging such a fleet as had been gather in Hampton Roads waiting on her. As you say it is obvious that the Monitor did not want to engage the Virginia one-on-one again. And after that first engagement the Monitor hid in shallow waters and under the guns of larger vessels and Forts. Which tells of their evaluation of the Virginia's power as a fighting ship. I believe that IF the Virginia had returned to Hampton Roads before the Union Rams arrived she may have upset the Union blockade in Hampton Roads and prevented "little Mac's" Pennsular Campaign from taking place.