"Got him on TCAS" is really the same as "I have him visual",
Riverboat, that's exactly the point; it's not!
Controllers may be able to offer a new opportunity for the following pilot to maneouvre behind the preceding aircraft if he has visual contact with the one ahead in an approach situation; thereby reducing the usual IFR separation hindrance required. Knowledge of TCAS contact doesn't create any advantage to a controller's work unless it is of course in an RA situation.
What is pertinent in this day and age is clutter of R/T frequencies. If everyone responded "Roger, Flyguy 123" instead of "Copied, we see that traffic on TCAS, Flyguy 123", the seconds saved would add up to useful useable frequency space during the working day. This is where we can all work together to enhance a safer flying environment.
I do however agree with you that we are all working toward the same end of enhancing safety, but sometimes kindhearted pilot's extra "reassurance" is not required when the controller is not trying to imply a risk of collision in the first place.