Back in the day we used to do a lot of narrative gaming (that usually ended up going down the competitive slippery slope). We tried the map route, but finally eschewed it for a branching tree of missions, sometimes official, sometimes fanmade, sometimes written by ourselves.
What mission to do next was decided by the winning side of the previous battle. The battles in the coming round had been chosen so that at least one of them gave one of the two armies a slight advantage over its foe. Nothing drastic, just things like night fighting for Dark Eldar, or deployment or mission types that favored certain armies or builds. Choosing the "right" mission was up to the players' "strategic acumen"
Later on we tried a different approach using assymetrical information flows, such as showing the missions only to the choosing player so that he could tailor his list accordingly, but that didn't quite work out as expected.
We also had a "strategy card" system similar to the one you devised. Sometimes the use of said cards was restricted to a specific mission just to balance things out. We talked about incorporating Kill Team "commando raids" so that a player could neutralize an enemy strategy card, but never got to implement it.
Another thing we also partially implemented was a levelling system for player
HQs. In the end we went with custom-built characters that could gain additional rules as the campaign went on. I recall one of my characters was a Big Mek that could upgrade a single Battlewagon to a fast vehicle!
If I had the time, I'd translate some of those old campaigns, put them up to 7th ed standards, and release them somewhere. In the meantime, hope this gave you some ideas!