I think it is unnecessary verbiage, and it does not add anything normally. As an ATCO you are required to monitor a readback, and if any element is readback wrongly or omitted, then you would be failing in your job as an ATCO if you did not pick this up and ensure the correct clearance IS readback. Therefore in the absence of any reply from the ATCO after the aircraft reads back the clearance, it means that the readback is correct.
I would only use 'Readback Correct' if the recipient had had more than one go at reading the clearance back correctly, or perhaps if their spoken english was not very good.
The colleges do seem however to teach trainees to do this all the time.