Most people with 20K in the market aren't using Coinbase. GDAX is also run by the makers of Coinbase and has much better capabilities, including bid/ask as well as better rates on trades.
I think Coinbase is great for newbie investors who want to throw less than 1000 dollars into the market and see what happens. I feel like most serious investors with a bigger stake are already trading on other exchanges.
More competition for services to appeal to newbie investors, and more people entering the market is definitely good for the crypto space, and I look forward to seeing what Robinhood brings to the table.
RE: This is the start of the "Race to the Bottom"!