I read recently that Richard Strauss said that conducting had to be a balance between "faithfulness to the score and inspired improvisation." Of course, Strauss was talking about improvisation of rubato, dynamics, emotional spirit, etc., not the actual notes.
Improvising actual notes, though, is a wonderful way to free up the spirit and one's creativity, even for those who are going to improvise only in private and stick to classical music in their public performing.
Free improvisation in particular can counteract the sort of forces I discuss in the following, which I also submitted as a comment on Greg's site:
Dull music-making is indeed a big issue. And the ironic thing is that conservatory training, the orchestral audition process, and most music competitions emphasize technical perfection, discourage genuinely individualistic performance, and are much of the problem.
The more charismatic an established performer, the more likely (s)he is to be ridiculed by teachers and by other players of that instrument. The more impassioned and original a young artist, the more likely a member of a competition jury is to be offended by the interpretation or stage presence and give a low score. (That's why I'm in favor of having competition juries made up of fine musicians who play a different instrument than that which is the focus of the competition.)
And the same sort of thing happens with the orchestral audition process, in which a committee has, usually, total say over who gets into the final round heard by the music director. The usual advice for people taking orchestra auditions is to be able to play everything with technical perfection, good musicianship, but little "personality." And again, the less bland the playing the higher the liklihood of offending a committee member.
When I was a teenager at the North Carolina School of the Arts in the 1970s, I had a cello teacher who encouraged me to play with emotional and physical abandon. I was overtly emotional and moved around a lot. Audiences and singer friends loved it. Other instrumentalists? Once I got into playing like this, some wouldn't even speak to me. I was (sniff) "acting." And sometimes in the heat of the moment I played out of tune. How very, very distasteful!
I recently attended a master class by a very famous cellist, now retired from performing, who was known for his rather reserved stage presence. As he does quite often, he devoted part of the class to making fun of players who show the spirit of the music in their faces and bodies. He did this by, rather comically, mocking this behavior while playing. I thought he actually sounded better. Whether he did or not, his students, and their students, are being taught that to be physically demonstrative is to be deserving of scorn and ridicule.
There are even lots of cellists still denouncing Jackie DuPre, who's been dead for nearly 20 years! And I never heard so many second-rate conducting teachers put down anyone more than Leonard Bernstein, not realizing that his "showmanship" sprang from genuine passion and knowing his scores inside and out, as well as a natural theatricality. Think of all Bernstein did for classical music! And to hear some people talk, back when I was a student, you'd think he was some sort of evil force.
So the bad news is in much of classical-music land, we are teaching our students to have a boring stage presence and exert social pressure on each other to do the same.