Stats- In the example jacjacatk provided, I defined success by team wins. There was a direct correlation between K% and winning percentage. For individual pitchers, I would say some sort of combination of ERA and FIP would be a solid measure of success in this particular scenario. There are proprietary metrics that I am aware of but unfortunately, those can't be applied here.
cabbagedad- My feeling towards "pitching to contact" really has nothing to do with scouting, to be honest with you (thanks!). To me, it's a pretty simple economic formula. The goal of the pitcher is to get the batter out. The best way to ensure the batter is out is by strikeout. The best way to reach a strikeout is by throwing quality strikes in areas that the batter has difficulty hitting the pitch. "Pitching to contact" implies an attempt to avoid making an optimum pitch and, as a result, maximizing the opportunity to induce the weakest possible offensive result. I understand the concept behind pitching to contact, I've just never understood why it would be considered the optimal way to go about achieving success. I indirectly touched upon this in my Master's thesis, which detailed the successes a pitcher has when facing a batter less times (Ie: less innings per outing). The single biggest jump in statistical results stemming from my study (which yielded data from 1992-2012) was K%, which, as noted above, correlates with a better pitching performance.
In the same light, there is absolutely no such thing as a waste pitch. Every pitch thrown has a purpose. And if executed properly, a pitcher's goal should be to minimize the batter's chances to hit the ball with authority. The best way to do that is to strike the batter out.