I may be wrong, here... but I think the change in Biome generation from 1.6.6 Beta and 1.7.3 Beta to 1.8.x will actually generate different SEEDs, than what you'd expect.
So I'd make a "fresh" copy of your world, and leave it 98% unexplored (as in, create the new world, let it generate chunks... and save... and then leave the world after you save, and don't return to it, until the update.
...and even then, it might not factor in the generations of structures... so who knows. Just don't be shocked if your favorite SEEDs no longer work with this update. I know mine won't (already experienced that on the PC side of the fence).
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