My two cents:
please don't ruin this beautiful piece with percussion! Percussion will just give it a cliche'd lift music jazz vibe.
What I am in favour of is after 2/3 of the piece, do something to provide greater contrast. Some subtle strings would be nice, but a piano part (sax tacet), in a higher octave, will add some extra 'magic'.
A key change would be possible too, key changes are not BAD, but playing the same thing over again in another key is cliched, and not the best example of effective key changing.
A key change AND a melody/rhythm change together could really do wonder to create a totally new mood to surprise the listener.
Keep it up, you guys are great at playing your instruments!!