I got the impression the repetition was intentionally there to force the player to adapt to their surroundings. The game design is trying to get you to behave in a more complex and f***ed up way by giving you the same problem repeatedly.
The first time you took on a convoy mission, it was a huge pain in the ass, right? I had to stack jeeps into the road, shoot up the guards from far away, run in, grenade, keep dodging bullets, etc. Then you unlock the remote bombs. Then you unlock the grenade launcher. Then the sniper rifle. By the time I got to the end game, I popped all the guards from half a mile away, waltzed right into the road, and blew the truck apart with a rocket.
The thing about Far Cry 2 is that if you're playing it on Easy, you don't really have to evolve. You can just plow around and the game will get boring fast. But if you have the game at a tough enough setting, it will continually push you to become more nasty. I haven't come close to beating it on the hardest setting, but you will literally have to light the grass on fire, wait for the guards to move away from the turrets out of fear, injure one, wait for his friend to come out, kill him, etc. etc.
I dunno, looking at that rant I'm realizing I just proved your point about having a lot of free time but I'll say this: it's hard to go back to linear shooters after doing a game like this. It's really refreshing to not have a game hold my hand all the damn time.