Phillipe: Excuse us if we get a little too carried away, it happens. Your harmonica, as it is, clearly does what you want it to do, and you should use whatever design you think works best for you.
Even for your current design though, overblows might still be something to consider. Each overblow would be identical to the blow note to the right, with the difference that it could be bent a little bit up or down for expression. In parts of the range, if the reeds are well set up, overblows can be bent upwards more than a semitone with some practice. It could also be used to reduce jumps, for instance having blow C and (overblow) E in adjacent holes.
You mention you've experimented with designs with and without valves, and one way to get the most of your tuning could be to employ
"reverse halfvalving": to use outside valves on every blow note and no valves on the inside for the draw notes. This would allow the valved draw bends you mention, but also overblows to get more bendable versions of the blow notes!
Brendan: Of course it tickles me! It would have full note bends on every note, octaves in adjacent holes (half of them two holes away if you exclude OBs..), over 3 octaves in 16 holes... It would even have
single-hole 3-note minor arpeggios(!) for every note, and single-hole 3-note major arpeggios for
every other note 
What's not to like? Most of this would apply almost as well to a halfvalved version.
I'd have the harp half-valved, so they don't apply to moi.