NL $100 ring flop bets

Hey everyone, love the forum, been lurking for a couple of weeks, and found it very helpful so far. Now I'm here looking for some help/opinions.

I seem to have picked up a habit from the last round of crap bonuses at Empire Poker. When the Party split initially happened, I'm sure most of you noticed that the games got tighter than a nun's legs.

I got myself to a very decent winrate simply pushing rocks around a lot. (PFA > 10)

Now I've moved up to NL $100, away from ex-Party skins, and am in a more normal kind of environment.

Problem is, I still find myself taking pot-sized pokes at flops I have no business bluffing at. I'm getting called down about half the time, and it takes around a 70%-80% (I believe?) success rate to make the practice +EV.

So my question is this:
What guidelines do you use to determine whether or not you should take a poke at a pot that you raised and missed the flop on, but has been checked to you and you're last to act?
(Holy run-on sentence, Batman!)

Thanks, folks!