One thing I do see with some regularity (at least from the pricing for where I fly from), if the fare ticks up slightly from a price I have been considering, it will often drop back down within a few days. This usually happens well out from the travel date and with good seat availability. I have also found when the fare is shown as "only 3 seats available at this price", that is often true until or unless more seats are released at a given price. When I bought back in May this happened and the fare never got back close to what I paid.

Like you, if I were considering a fare and saw it drop $100 (or even less), I would be all over it as it can easily go up.