Musical achievement, practice, expression and timbre.

I'm reading Sloboda's big book. I would like to jump a bit and talk about the relationship between practice and musical achievement. Let's start with three things that were discovered through the Leverhulm study:
1) Early parental involvement is very important in musical achievement. If you are a children and your parents talk with your music professor and if they really want to hear what can you do today with your instrument, you'll probably have more motivation to practice.
2) Self-motivation to practice is really important as adolescence progresses. Now it's time to work because you love music, not because your parents want you to do it.
3) External circumstances are really important. Studying in summer will not be as much as enlightening as studying before giving a concert.

Now let's say a word about our subject. Timbre microstructure is one of the elements that will be affected by the expressive devices a high-level performer will use to add value to a musical score. What about high-level composers and producers?