Is your goal to reduce global temperatures? If so, it needs to be a sustainable effort. You don't get sustainable effort without economic viability.
If your goal is to dramatically reduce temperatures in the next 5 years, why not dump SiO2 in the atmosphere? That would bring the temperature down pretty fast by reflecting out sunlight in the upper atmosphere.
But if your goal is long-term change, we need an approach that works long-term.
Edit: sorry I forgot to mention your point on coal vs natural gas efficiency, I didn't realize it was not that much gain. I still think it's worth it though, since it's still making progress.