My main personal interest is in putting on some small hedges for some currency exposure in one of my accounts, so I'm not too concerned about liquidity and paying a big spread.
However, I don't think you can necessarily extrapolate out the volume decrease from the full size to the half size and say the micro will get even less volume. A perfect example is the Nikkei 225 contracts in Asia... there are three of them, a full, mid-size, and mini, and guess which one gets the most volume? The mini. Even though each tick is less than $5 USD, and the round trip commissions at IB are around $3, it still gets more volume than the other two combined (didn't check the figures but it sure seemed like it from my experience).
I think it will be fun to watch and see if these things can pick up any steam.