Likes of Mendis and Murali are naturally gifted cricketers, and their techniques and style of bowling are more self developed then anything else, the same too could be said about Warney, and in his case the guidance he got from Jenner only helped him further develop strong points of his bowling.
Though I don't think any of these spinners would have been effective had their individuality not been respected, when I look at most of current Australian spinners, I don't see that to be the case.
The things at the coaching level just don't seem to be going right because from what I have seen and read about this, every spinner in Australia is being taught to follow the same set of stereotypical rules while learning how to bowl spin, without taking into account what their strong and weak points are, and as a result lot of current Aussie spinners are pretty similar to each other in the way they operate.
The spin coaches have also failed to iron out some basic technical problems that the spinners are having, White is a good example, there was a time when he was working hard on developing his bowling with Jenner, but he failed to do so, because with a bowling action like his, its virtually impossible to bowl accurately or get any sidespin, and it pretty baffling a spin coach couldn't help him correct such a obvious error.