I don’t think anyone could give you an exact measurement, however, ASICs definitely affect the price of a coin when they first start up.
Since I don’t have time to attempt to put together a bunch of research, think of it this way.
It’s the gold rush, and everyone is mining wish shovels. All of a sudden, someone has a backhoe. Since they are orders of magnitude more efficient, they will begin flooding the market with more gold than all of those with shovels. At this point, it’s a simple supply and demand equation. Those with the early equipment want to ensure they hit ROI, which in theory should cause a race to the bottom by those bringing in the most ZEC (those with Backhoes in the analogy, or those with newly created ASICs). This will stop once that bottom is hit, and then the market will continue back on its trajectory, and those mining are it for ZEC, ROI, and Securing the network.
I would argue a lot of the GPU miners were mining for coins to own, while those with the first ASICs were primiary worried about fiat currency.
This is speculation, but what I truly believe is happening. I did it myself with the L3+'s, and saw tons of others doing the same, so I know it would also be occuring for ZEC.
That all said, it’s a one time shot from GPU to ASIC, and then smaller impacts and ASICs improve their hash rate. But the jump from GPU to ASIC is a big one, and there was lots of short term money to be made.