I think too many teams try to make up points with the 2 pt. conversion too often. I've noticed that games usually turn out where had they gone ahead a kicked the extra point they would have been in a better position at the end of the game.
Let's say for example, the Texans miss the 2 pt. conversion, like they did. 21-16. Detroit goes down and instead of scoring another TD, the D holds them to a FG. 24-16. Had the Texans kicked the extra point, they would only need 7, instead of doing it the hard way and having to get a TD and 2 pointer. That's the way it seems most games get down to when teams go for 2 with a whole lot of game left. I have no stats on that or anything, but I've seen many a game where a team gets to the end needing a 2 pt. conversion after failing earlier in the game, when had the kicked, all they would have needed is 7. And it seems like it happens more often than not.
I think you should never go for two unless it is at or near the end of the game...say less than 5 or 6 minutes. With 12, 13 minutes left, there's just too much football left to be played.
Points are hard to come by in the NFL. Take the easy ones.