though i realise i'm arriving a bit late in the game, as it were, and
though i haven't fully read the entire thread, one particular theme comes
to mind.  i am referring to the theme falsely attributed to corelli by
rachmaninov in his corelli variations op.  42; the 'la folia' theme -
also used extensively in liszt's rhapsodie espagnole, and of course by
corelli himself...  and speaking of the dies irae mentioned below, i
believe no one quoted that particular chant more than rachmaninov himself
- to the point that i believe he was perhaps slightly obsessed with it!

as a pianist composer myself, and having recently begun a project
of writing piano improvisations which i eventually hope to auto-produce
(as a recording), i can't help but notice similarities in style between
my own compositions and those of other composers.  the first four published
on my site include one which i had initially conceived as an 'a la maniere
de ravel', hinting at ravel's own two 'a la maniere de borodine/chabrier'.
much to my dismay, though, i now find that it much more resembles debussy's
style than ravel.  this disappoints me because i've always preferred
ravel to debussy!  i subsequently decided to re-subtitle it as an 'hommage
a debussy', as debussy's own 'hommage a rameau'.  another improvisation,
though more akin to villa-lobos than schumann, is subtitled 'eusebius'.
the point is, one can capture the ethos of a particular composer's style
while emulating that of a very distantly related composer - or one whom
is not at all related to the latter, or furthermore, in one's own affirmed
style.

for those of you interested in listening to the first four of these
improvisations, please feel free to visit my page and let me know whom
*you* think it sounds like!  the link is noted below:

   http://web.mac.com/solaneto

best,

olivier solanet
NY, NY via Paris, FR