I would like to propose that in most 4X strategy games, war is too aseptic. You can build a super stack or four and sometimes they never lose a unit for the life of the stack. In my opinion, battles should be more down and dirty with both sides taking loses.
In part this is designed into a game with the damage model. I'm not advocating that the combat model should allow lowly spearmen to take out battleships... er dragons in one shot. I'm suggesting that all attacks should have some 'ooomph'. When battles are started, both sides should expect that when the other side launches a volley of arrows, a fireball, or dragon flame... that that HURTS and some casualties will be taken even if you expect to win at the end.
I'm not just advocating this for flavor. I think there are some game benefits:
1. Less emphasis on superstacks walking over everything
2. More variety of units entering into a game since fewer units will 'live' throughout the game
3. Make units that do survive more noteworthy
4. More interesting unit mix - Example from XCom -> If you put all your Colonels and cammanders in the same squad (until you got power armor), it was unexceptably costly since you were bound to lose some of your most experienced troops. So I always used a mix of experienced and less experienced troops.
5. Makes weaker units more relevant.
6. Need to coordinate and support defense more. In other 4x games, park a defensive unit behind a wall and you can almost forget about it.