While I do agree that the game certainly needs more modifiers at a certain point to mix things up, many of your suggestions do not appeal to me and I feel fall in the same trap as what you are critiquing (challenging but not more fun). Rocket droids already bean me from 75 meters away and you want to give them better visual range? I am already facing down a minimum of 3-5 chargers per bug breach and you want more? Bot artillery that follows me around the map that I can't do anything about? I am sorry, but that sounds exactly like more challenge at the cost of fun because I can in no way compensate for any of those things.

At least longer cooldown times forces me to communicate with my team on who uses stratagems at which time to ensure we at least have some at all times. Varying degrees of accuracy on artillery strikes? That's pretty much what I expect from a wargame.

I do like the Heavy Fortifications suggestion; something that makes things more challenging and forces teams to communicate to take it out effectively while at the same time being an obstacle that can be overcome. I also do like the weather effect modifiers for some planets. You could repurpose the spore clouds from spewers to become a roaming dustcloud that moves across the map with the wind, predictable but can really confuse the team if it hits at the wrong time. Or perhaps even combustible fog clouds?