Hi, I've been there too. Traffic is obviously too far away to take reasonable photos from the beach, however you do see the ships passing in both directions. Afternoon view from Mirador del Estrecho https://goo.gl/maps/bMyFMA5Xa1i8S5vm7
is impressive (again not for taking photos of ships). On the fastferries to Tanger, there is indeed access to the outside deck, but you are unlikely to hit any (interesting) traffic at the exact moment of crossing at 30+ kn, so this would be just for fun...
There are whalewatching trips from Tarifa port which take a couple of hours and went right in the middle of the straits; apart from seing some dolphins, this is certainly a very good position, unfortunately didn't do it sofar.
Also a nice daytrip to Algeciras with (slow) ferry roundtrip to Ceuta can be done, passing the port of Algeciras, Bay of Gibraltar and the Straits with better chance to see something passing than on the fastferry. So for a couple of days, would definitely recommend the place.