Okay so briefly:

1. Our opponent's flop calling range contains a lot of air, but also his entire range of "good" hands.
2. Because of the large amount of air in his flop calling range, we can [semi]bluff the turn a lot.
3. This suggests that we should consider balancing our bet flop/bet turn range with stronger hands.
4. Doing so would be useless if he didn't have very many hands at all in his flop calling range that are calling a turn bet since we'd rarely get value. (ties in with your last paragraph)
5. Sort of a side point that hung me up for a few minutes, even though he has these "good" hands that are calling two streets, there is so much air that bluffing the turn is still profitable.

Edit: Actually now that I look back at it after going to the bathroom, I don't think #3 necessarily belongs. I think balance is the wrong word and idea to use here. If I had to rewrite #3 I would say something like, "Figure out what we're doing with our good hands on the turn." The answer then becomes a function of what his turn range looks like and how he's playing it, like it should be.