I can only tell you what I do. If it's a price i expect to pay, I book asap to get the flight date and time. If it comes down, they will give you a voucher that is good towards another trip.
I have never had a price actually come down on me. While they might come down, it is never for the flights I want or am on. We are going the end of August NY to MCO $171 round trip. While they have been advertised $130 recently, when I called the $130 fares were not good for when I wanted to go and any seats left on my flight were way, way higher. So I did the right thing by booking last December for my August trip. For me to get the $130 I would loose 3 days of my vacation, a change I would not want to do.
If you are locked into flying on certain days, or need certain times then I'd book early at the best rate, if you are more flexible you can wait. I like knowing my air is booked and I have a seat.
Have a great trip.