Awsome topic! I think a great example of the "Coinbase effect" comes as a rumer that Ripple might be listed with them and the price jacks up and then when that rumer is reported to be false comes the crash. It seems to me that they have too much power and I for one am looking forward to them having a little competition in the US market for being the most legitimate Exchange. Competition will bring about more equinimity imo and maybe it will help lower their ginormous fees as well.
I would completely agree with you on token rumors. Anytime there is a hint of a token getting added to Coinbase, there is a noticeable jump in price. The competition is out there, but yes, it does seem CB has the lion's share in US crypto. However, I think this might be changing, and we could consider the crypto - internet analagy here. It seems apt to say that CB functions as an "AOL" or maybe "Netscape." They may be the pioneers, but its hard to stay on top.