The S-300 is entirely compromised it seems. Many times it’s just flat out been ECM’d. I think these next ones are probably not much better against ECM. The USSR/Russians never really did much combat against ECM, and they always got slammed in real combat. Often to the point where their systems were probably worse than having nothing at all.
Turkey, Israel, Italy, France and even Spain and Germany have submarines in the Mediterranean sea. The latest Israeli and German U-boats are equipped with a mast-mounted gun system http://en.wikipedia.org/wiki/Rheinmetall_RMK30. The submarine can attack a vessel with that gun while staying submerged. Try to hit a submarine with a radar guided missile.
On the other side you don’t need to get so close to Syria to stop ships on their way to Syria.
I don’t think so. The problem Syria has a contested ground, not skies right now. You simply can’t operate such a sophisticated system like S-300 in an environment like that with rebels around.