I've been reading posts lately by conductors on a list-serve sponsored by the League of American Orchestras regarding a whole host of issues - from programming ideas about cars to the meaning of reuhrtrommel to dynamic markings in the Brahms Violin Concerto. It has been interesting not only because fascinating threads of thought emerge from a variety of people, but also because some of the sources of these ideas come from numerous well-respected teachers/conductors who have differing ideas and solutions to particular problems!
Just as history seems to take turns with increased scholarship, the interpretation of musical markings and meanings sometimes is evolving as well, especially when it affects interpretive decisions. I have always thought that having as much musicological material at your disposal is of the utmost importance, and being sensitive to the wishes of the composer with this information is very helpful making determinations that on the surface can seem subjective. But I've also discovered, having worked with multiple Pulitzer Prize winning composers, as well as other composers who are quite accomplished, that these great aural painters change their minds about notation and passages pretty uniformly over time when revisiting works. In other words, if I've conducted a piece multiple times, these composers many times attack questions with different answers after a couple years pass.
Why? Because it's human nature to evolve. Do you listen to any piece of music you love with the same ears as when you first heard it? Neither do great composers. They are growing, learning, and changing both professionally and personally (for artists, the professional and personal are absolutely intertwined!). While I think making reference to performance practice is necessary, and also thinking about why a composer makes the choice they do is an excellent way to get into the sound on the page, ultimately it will always come back to how the music expands in live space - not between one's ears - but in an acoustic with a particular group of gifted musicians. Change one musician, and the whole paradigm shifts, and the rehearsal process and performance will be different beyond the notes that have been created by these amazing artists.
I think intellectualism in music is important, but to me, it will always take a back seat to a humanistic approach. How does a phrase become beautiful as one breathes? How does the dynamic relationship between musicians and audience affect a composer's intent? These are living, breathing questions that are answered daily on a human level - of course with deep thought, but ultimately, with a nod to the inherent personalities of those making the sound.