ZEC and Ethereum will level out to be about even profit wise, you will always have a large group of people jumping ship from one to another causing an imbalance between the 2,
My predictions from a few days after Zcash launched were it will come down to meet Ethereum, Why? Because when it's more profitable, everyone leaves to mine it, flooding the market, dropping price, less demand for buyers and more sellers just selling at market value chunking into the buy orders to offload coins. Simple supply and demand.
Once price drops, people switch back to Ethereum when it once again becomes more profitable, swinging the balance once again, George of the Jungle comes to mind!
All in all, Zcash of course will drop in price, it will continue to drop as the block rate keeps increasing. It's block rate started low and is increasing, hence more coins are available, you can't expect more and more coins to be rewarded each block and price to remain at the same values, just won't happen.
Either way, it opens up a longer period of mining for all GPU users

Be happy.