Can situation 1 & 2 be +EV for both players? I think this is impossible. In a 0 EV situations you are probably better off waiting for the turn to reduce variance.

Usually what happens though is there is a raise or two and we get committed one way or another.

metagame and balance (getting a/i with sets and combo draws on flop) are important if you play decent players repeatedly (i.e not so much at 50NL)