At first I freakin' HATED on the respawning guard posts, but you have to admit: if those guard posts were permanently destroyed, the game would get pretty lonely pretty quickly!
One thing that might have been better is that guard posts respawn only once per day, for instance, so that in a given day once you clear a spot, it's clear until the following morning.
If they did it that way, it might be interesting to have a minigame mode: "Clear all guard posts in one day." Or even an ... achievement!!
As I wrote on the xbox forums years ago, if you find this game boring, just pick up your pace: try and power into a mission area and finish a given mission in as short a time as possible. Don't hang back and pick people off: just rush in and mix it up.
If you do that I think your boredom will go away. Heck, even if you're not ON an official mission, pick ANY one of the "named areas" of the map and power into it, try and clear everybody out as quickly as you can.
Or try and do a named area with just a pistol... or just with flamethrower. It changes things up when you have to constantly stay out of sniper and rifle range and run right up to people and set the entire place on fire.
Or... do it all with the machete!!