Number one: President and Security class is only for registered players, and President slot is free to everybody. at least registered players have a clue or a bit of brains to know what to do instead of shooting each other in the spawn or car jacking the President..
-1. It happens sometimes, but usually newbies are trying to protect fairly. I can understand you, but it is not a reason enough to put such restrictions.
Number two: Every time a new President spawns, re-spawn all the vehicles in his spawn as well, a few auto-msg's for the Security class would be good too (only Security can see it) something like "Defend the President from Terrorists and Civilian attacks".
+1. As it was correctly mentioned above, respawning cars isn't really a good idea, better to add more of them to every president spawn.
As for the announcements and round-sounds... I'd say they are fine to be displayed to non-registered players; for lvl 1+ they should be toggleable; for lvl 1 they are enabled by default, for lvl 2+ they are disabled by default. So,
+1. Maybe it would help newbies to get started. And if they got annoyed, they should play only for 10 minutes to register and disable it.