Sometimes the need for drastic measures...
I too would rather see the graft removed; but as mentioned above, the long 90 degree bend in a trunk that is the same diameter for much of it makes it look like green growth at the end of a couple of bones. So I can see why the previous owner did what they did.
My thoughts (those of a beginner) would be to leave the shimp until I could find a Cal juni that I could maybe take a cutting from (next time your in Calif...) and try to graft that in the shimp's place. Even then the possibilities for a cascade are years in the making.
My other thought (one that I would want if it were my tree) would be to try and create a shorter trunk (after the bend, where the shimp graft is) by removing the shimp graft and doing an air layering to get new roots. This would hopefully create more options for you, and you still have the wonderful jin in the upper part of the tree and the two nice areas of growth to work with. To see what I mean, I took some liberty and Photo shopped your 1st picture.
I realize that both of these are quite drastic and difficult and would take years to achieve, but looking at what you have and what your thinking of doing with it, I'm hoping of enlightening you to other possibilities.
Best of luck in what ever you decide to do.