I've been working, with limited success,on playing Jessica by the
Allman Brothers on the harmonica. It's okay, because I'm having fun
with it. Also, since it's in A, there are a lot of high notes which
sound thin, so I've been having fun trying to hit them as octaves
instead of single notes.
So last weekend I was playing with a friend and we got into a long jam
in A and suddenly I was playing differently. The music just poured out
and we got into a groove that went on forever.
So even if you practice on something that doesn't have a direct
correlation with what you're playing, it can help improve your
playing.