If you have reused addresses, you have already negatively affected your privacy.
Not necessarily.
Imagine if you and I had a
private deal and you gave me your address and I sent you 3 payments on 3 different occasions. As far as
the rest of the world knows an arbitrary address received coins from 1 to 3 [sending] addresses but they don't know if that address belongs to you. Consolidating those 3 outputs doesn't change that either.
If you sent me three transactions to the same address, an observer would, at a minimum, know that I own the sum of the transaction amounts received from you.
If I asked you to send the transactions to unique, and unused addresses each time you were due to send me coin, an observer would only know that addresses "a", "b", and "c" had received a particular amount of coin. Depending on your privacy practices, an observer may, or may not know the coin was sent by the same person.
You are correct that consolidating three outputs all sent to the same address will not further reduce privacy, but that is because privacy has already been incrementally reduced via the address reuse.