As you say, you are above the MATZ so you don't need to call them up..
However in my opinion, I would consider it good 'airmanship' to call any ATSU you are passing near or over even if not obliged to. As Gertrude the Wombat said he was near a MATZ and not in contact but probably would have made things easier for all concerned if he had been (not having a pop, just using it as an example)
I would and do always call an airfield Im over flying and as for any conflicting traffic info.