GendoIkari, I agree with your second point. Eventually, the novice player will get a can't-lose Mountebank/Lighthouse opening that you just can't do anything about. The wins don't budge your ranking northward, and the losses send your skill plummeting and uncertainty up. Meanwhile, the wins inflict you with just-won second-seat status against the next player that comes along.
As to how long to keep playing in the face of a bad night, interesting point. I guess that probably depends on each player's individual reactions more than I might have thought at first.
On most days, I play for about 40 minutes to an hour, and I set myself a daily limit of 4 losses. 4 losses in that time mean I'm having a horrible day, so I just stop and go do something else, and try again the next day.