My answer to the latter group: sorry kids, you're not going to be the next Bell, Ma, Stoltzman, or whatever great player of your chosen instrument. The reason? Simply put, you'd have to be a student at one of three schools: Eastman, Julliard, Curtis, to have a prayer. AND, you ought to be glad to have as good an ensemble as you have to learn the repertoire with, AND you need to be thankful for the presence of a better-than-average regional orchestra that you might be lucky enough to perform with. There are an extremely limited number of seats available in all the orchestras in the country--big, small or otherwise--and this is probably as good as it gets.
As for those endless hours of practice? Most of you are wasting several hours/day. In a January 25, 2012 article in Time, author Annie Murphy Paul notes that one must practice "deliberately". "The difference between ineffective and effective practice means the difference between mediocrity and mastery. If you’re not practicing deliberately — whether it’s a foreign language, a musical instrument or any other new skill — you might as well not practice at all."
She cites cognitive psychologist Anders Ericsson's 1993 paper that seems to finally be making the rounds. Paul goes on to summarize Ericsson's work, "Long hours of practice are not enough. And noodling around on the piano or idly taking some swings with a golf club is definitely not enough. “Deliberate practice,” Ericsson declares sternly, “requires effort and is not inherently enjoyable.” Having given us fair warning, he reveals the secret of deliberate practice: relentlessly focusing on our weaknesses and inventing new ways to root them out. Results are carefully monitored, ideally with the help of a coach or teacher, and become grist for the next round of ruthless self-evaluation." More of Ms. Paul's article can be found here.
I have noticed just the opposite to be true of some of my students, colleagues and even my daughter. It is as if all have the mindset that, if they just play a passage (or a piece) enough times, it will magically become music. Obviously, nothing could be further from the truth. We need to teach students how to practice, how to examine their own performance and correct errors in search of the end goal. It is only then that their practice might--just might--get them to Carnegie Hall.