I think 30-50 dives is enough - you dont have to be the "superdiver" to carry a camera, you just need to show a little care or be directed to show a little care so you are more aware. Additionally not all dive sites are coral sites - indeed some of the best sites I have ever dove have been devoid of coral naturally.
Carrying a camera makes you dive a completely different style to a "normal" diver and you can learn bouyancy control from that - lets be honest a large number of dive guides lead a pack of divers on what amounts to a 200 yard sprint at best - you can maintain correct bouyancy even if you weighting is miles off so long as you are moving forward fast enough. It could be argued that carrying a camera will increase the rate at which a diver will learn "advanced" bouyancy skills because of the diving style change.
Just my opinion.
Carrying a camera makes you dive a completely different style to a "normal" diver and you can learn bouyancy control from that - lets be honest a large number of dive guides lead a pack of divers on what amounts to a 200 yard sprint at best - you can maintain correct bouyancy even if you weighting is miles off so long as you are moving forward fast enough. It could be argued that carrying a camera will increase the rate at which a diver will learn "advanced" bouyancy skills because of the diving style change.
Just my opinion.