I think it's an interesting pricing model but I don't think the current game will convert well over a longer period of time. New players will pay $2, get wooped on by veterans and probably never play again. The veterans will try hard to win those noob games to earn the free games. This could of course be thwarted by a ranking system.
Sure, I'd probably pay 20$ to continue playing the game indefinitely but I'd be much more interesting in different game modes. The tutorials were a lot of fun. If there was the ability to create maps and scenarios and even the odds by creating a custom line of specialists choices or having all of the players have the same exact specialists options, these things would increase the life of the game. Also, ranking system is huge as well as game modes like Capture the Flag or Coop maps, time delayed outpost destruction, public chat only game mode, no gifting game modes etc..
Another option that would be popular is the Free to Play model. You'd have to really focus on what you could provide a paying player that wouldn't imbalance the game. Ideas for this are:
-Free player can zoom 24 hours using the time machine, paying player can zoom 48 hours.
-Free player can't see the upcoming specialists hires until they are available, paying player can see the next available specialist hires 18 hours in advance.
-Free players can't join tournaments, private games or custom play. Paying players have access to custom maps, tournaments, and private games as well as in depth specialist reference.
These are just rough ideas but what it would provide is a more solid player base for everyone by still having a good amount of free players to boost the number of games as well as word of mouth and provide for enough public games so the paying players don't lose interest by playing against the same people.
Keep in mind, whatever IAP model you use, you need to focus on marketing. No matter how you really price a mobile game, the only way you'll make money is by marketing to the most people as possible. (Source: I work in mobile game development with one of the largest distributors on iOS and GP. One solution to this is publishing. We publish outside games, I don't think Subterfuge would fit into our model but if you're interested, PM me.)
I hope this helps.