This is definately a rule that has been long needed for the game, but without any form of defence for Gibraltar it seems like an easy take for the Axis? If Germany is able to wipe out the U.K. fleet on G1 as people are suggesting then it sounds like an easy grab for Italy that has long lasting consequences for the Med.. G2 would have perhaps a fighter or two landing there thus ensuring a real fight for the allies to retake it and keeping the Italian fleet safe from Allied Naval units. It's like fortifying the Carolinas on PAC40 it can hold back the Allies for several extra rounds that make all the difference.
Yeah. Historically it wasn't easy to take Gibraltar at all. It was impossible to amphibiously assault it (because of the almost vertical and heavily defended cliff) and even a paradrop would have been extremely difficult. The only truly feasible option would have been an attack trhough mainland Spain. Unfortunately for Hitler, Franco categorically and repeatedly refused this as he did not want to be involved. I wish they had therefore made it a bit harder to take Gibraltar..But hey, it's an improvement from the way things were!