ZvZ: Does this only work in low leagues?

Day[9] had a daily a short while back about the state of ZvZ. The games he used (I forget who played them) played out like ling/muta races, in which both players tried as hard as they could to win in either or both muta count and ling count.

That style is fun for a little while, until the adrenaline stops working. Not to mention, a couple of banelings can ruin your day, so it's a pretty volatile approach.

Anyway. In Silver league, that strategy plays out all the time. Since neither of us can micro, the baneling volatility is especially strong (lol). So what I've been doing is monitoring his base with overlords and then changelings while I drone. The second he puts down his spire, I throw down some spore crawlers at each base and then start churning out Hydras. Since I've been upgrading my lings anyway, the ground armor problem is already solved--just have to upgrade ranged attacks. Then, I wait for the inevitable muta attack, and defend with a hydra army backed by spores. If he's not terrible, only a few mutas die before the pack flies away, but then I can give chase and rally hydra reinforcements and force a GG.

This seems to be possible for 3 reasons:

1. Massing hydras is quicker/cheaper than massing mutas

2. I'm focusing on only ground upgrades, while he's dividing his upgrade bucks between ground and air

3. I can poke overseers into his base every now and then to see what's up (if he went mass roach instead of muta, then I don't think hydra would be a good choice)

Is this a viable counter in higher leagues? Or can a better player simply control Muta/Ling in a way that makes the hydra counter irrelevant?