when do you value bet the river without the nuts?

Ex:
Flop top set with Ace high flush draw on BTN
Bet small
get 2 callers
Str8 card hits the turn
checked to you... bet 1/2 pot and get 1 caller
river is blank
checked to you ...
1) do you bet the top set even with possible straights on the board?
2) What if villian had bet into you on the turn... you call ... then he checks to you on the river. Still bet?

Betting the river could be +EV when opponnent has 2-pair or lower set... basically if you think you have the best hand go ahead and bet about 1/4 pot. If you get re-raised just fold everytime because they probably have the nuts. For the most part I have just been checking alot on the river. As long as you are right the majority of the time about having the best hand it should be +EV. However, even if you are correct 70% of the time you would still need to get a call 50% of those times by a weaker hand which might be difficult to obtain. Thoughts?

i think it depends a lot on the site and the players. basically, it's read dependent.

for example, i find that at party, there are certain players who consistently SD with less than the nuts. i'll value bet these people. there are others who are just nutpeddlers -- i don't value bet these people.

some other sites may have lots of people who SD with less than the nuts. value bet these people more often.

i realize that this isn't an "easy" answer, but i think that it's the most accurate.