I've played AI War for about a year now. so heed my word!
Although AI War is designed to have great multiplayer mechanics, this is in addition to the solid single player experience. In multiplayer, some changes are made to tweak the difficulty to make it appropriate. But apart from the social experience of co-op, you are not missing anything.
If you already know you are comfortable playing single player, I 100% recommend a purchase. If you like to play solo, you lose nothing except for the blindingly obvious (not playing with other people).
I'm more of a co-op guy myself. I like to play with a friend, and I tab out all the time to read forums. Its very casual for me, although I do play on the higher difficulties so its not like I don't pay attention.
I've put many, many hours into this game. Re-playability will last you for years. And that means you are getting great value for the purchase price.
And these developers work with the community to make the game better and fix bugs all the time, responding personally to many topics. Although they are busy!