BaroqueBass-
...you're forgetting, I'm a tone-deaf weasle.
That said-
Certain instruments do lend themselves to certain keys easier than others(guitar keys=E, A, D, G; horn keys=F, Bb, Eb, Ab; drums= uh,...nevermind).
I'm not sure there *IS* a "difference" bewteen Dmin & Emin. Color & timbre DO COUNT for something, though. I was more discerning about such matters when I actually played guitar(certain keys & voicings, in particular, did sound "better" in certain circumstances. I'm still very "anal" about HOW a chord is voiced!).
A Rock/Funk composer may select Emin 'cause he knows/wants that low thump of the bass. A Rap/Metal band may eventually transpose the same tune down to Dmin 'cause they want the additional thump of a de-tuned bass/synth.
Kinda weird, though, that some of those early James Brown/Bootsy grooves are in Eb? Too, Stevie Wonder wrote a ton of stuff in the "FLAT" keys. Did those keys sound "better" to Stevie or was it just 'cause those are the black keys on a piano & thus easier for him to find/play?
Also, there have been tunes that were written, then recorded in a specific key, & then ALTERED by some studio mumbo-jumbo. "Beat It" by Michael Jackson is an example; the tune is in "Em" yet sounds closer to "Ebm".
The Beboppers borrowed the changes to many a standard...I'd bet Parker, Diz, et al changed the key to fit their needs.
Not sure where I'm goin' with this(rambin' big time, sorry); maybe it's more of an issue with Classical composers. Jazz, Rock, R&B, Pop, etc composers seem to write more on what's relatable & easy to them(ie their instruments, vocals,...).