Sugar- I dont think there is a pattern. The only thing i notice is that prices change nearly hourly for flights with in the next month and a half. IF you are booking further out like i want to (memorial day weekedn) they tend to be stable until getting to the 1.5 month range.
A few people from my group booked for the memorial day weekend and 10 minutes later the departing flight shot up $50. So i think they have a program that sets price on the number of empty seat to the number of days until the flight departs. If a group books for flights next weekend you should expect it to go up, unless there are a ton of open seats still.
If you go through booking and select seats but dont actually buy a seat (you select a seat before you pay) you can see how many "avaliable" seats there are. I am not 100% sure if this is accurate because it could simply be people that paid extra for a reserved seat, will show up as a "unavaliable" seats. At any rate, i use that as a gauge to how many seat are left on the flight.
Another thing they do is have the departing flight be cheap (like $29-69) and the returning flights for the next 4 days will be expensive.
When they run the "fly free" promotion which is when you buy 2 tix and a hotel one of the tix is free, they usually jack up their prices to of-set the difference and often its the same if you book the seperately going through Hotwire
or priceline...or you can get a better hotel with hotwire
for the same amount of money total. The good thing about that deal is if you are going with an even number of people, you can go two per room for the same price per person as 4 per room, therefore getting an extra room. For instance, 4 of us in December, we flew out of CID, for 3 nights, we stayed at TI for $253pp. It was $253 pp if we booked as 2 seperate parties, or as all 4 together. If you book seperately, each couple will get their own room, whereas together, you get 1 room.
I watch allegiant at least 2x daily for flights. These are the things i noticed. You just have to keep watching.