Need help designing power distribution system
I guess 4 A step-down converters are easier to come by than 32 A converters. Here are some other observations:

Each Li-Po cell is 3.7 V only when half-charged. The full range is 4.2-3.3V, thus a 4-cell battery like the one you linked will give up to 16.8 V, not 14.8 V. You could use a single 8-cell Li-Po instead of two 4-cell, but Hobbyking only lists a single 8-cell model so they might be less common.

You could use even fewer or even a single battery to power all solenoids to cut down on complexity/costs. I don't think the current is too high, especially not for a short burst of power. Keeping track of the charge of 8 or 16 batteries would be a risk, not to mention a lot of work. The batteries will degrade if stored at full charge, so just putting them into storage and preparing them again would be some work.

On the other hand, perhaps you're looking for redundancy. Consider what happens if one valve fails versus if the whole solution fails. You would have an easier time adding separate redundancy if your primary solution only has one 8-cell battery.

Another thing to watch out for is back EMF when shutting off the solenoids. I image the resulting voltage spikes can be massive if there's no protection.

Sounds like fun!