Follow this: Zimmermann career K ratio plus Zimmermann GB/FB career ratio= really good pitcher. Doing what he's doing = really good pitcher. And, 2015: virtually no change in the above career norm.
Now you say doing what he's doing is "a bad thing." Do you see the analytic tension there? He's been doing the same thing in these metrics for years--and has been very good. So, make no sense that what's good will be bad doing the same thing. You say you don't care about that. You should. It works for him.
Here's Lester compared to Zimmermann from 2011 thru 2015 using your preference, fWAR. This is ERA, FIP, x-FIP, f-WAR:
Lester 3.58-3.45-3.51-18.6
Zimmermann 3.10-3.28-3.58-18.5
Finally, $10 per season difference between two players for 5 or more seasons is a big deal. There are numerous player X vs. player Y decisions that an organization has to make. You cannot run a club and say 50% cost differences between player X and player Y isn't significant. Tell that to Theo and see if he'll hire you to help with personnel decisions.
It works for him at his current velocity. As his velocity decreases his margin of error will decrease to where he can pitch. It is much worse for a fly ball pitcher vs a ground ball pitcher.
I'll take Price over Zimmermann, Wada, Motte, Soriano or Zimmermann and Jackson.
If Price had a 2 mph drop this year, his strike outs dropped and his numbers got worse I would have similar concerns about giving him a large contract.
Comparing non-league park adjusted numbers is unfair. Zimmermann has pitched in the worst division in baseball. When you league/park adjust Lester is better. Lester also has a much higher GB% and strikes people out. He will age better.