Just my personal opinion is that since you should be eligible for an upgrade, I'd recommend that you get the M9 when it official goes on sale at Sprint.
Last year, I upgraded from the M7 to the M8, and there was a big difference. Larger screen, and better performance.
Personally, I'm not going to be upgrading this year, because the M9 is very similar to the M8. But, I was still on the M7, I would certainly upgrade to the M9.