Nothing wrong with .1 atmosphere of methane that .1 atmosphere of anti-GHG won't solve for you.
Incidentally, this ties into a suggestion I have for terraforming: Instead of the formula for greenhouse factor being min(GHG + 0.1*Other - aGHG, 3) I'd make it max(min((GHG + 0.1*Other)/aGHG, 3), 0.3).
That way, raising and lowering temperatures would be roughly equally challenging. Instead of the current situation where it takes three atmospheres to terraform Titan into something resembling habitability, but only one to terraform Mercury, despite Mercury being off the sweet spot by a much larger factor.