While good micro makes your fleets fight better its NOT what is going to win you the game. Its only a facet of the larger picture. What really makes or breakes your game are the decisions you have to do at strategic level. How much do i invest into economy? What kind of tactic am i going to use? How much do i spend in research and when and why? Am i going for colonizing and booming or do i pursue a more agressive and direct approach´?
Some will disagree, but, in online multiplayer, I find this to be false. When I lose, I almost always lose because the dude either has better clickfest abilities, or he is better at something else that is NOT related to strategy, but I rarely lose to strategy. In fact, often in an objective analysis, my strategy was much better, and this is born out through certain measures such as having many more planets, a better eco, etc. (I know those things don't necessarily always mean I had a better strategy, but they frequently mean it).
I used to be a rather avid chess enthusiast, along with a friend of mine. We played quite a many games over the years, and studied the game to some degree. Similarly, I almost always lost chess games due to tactical mistakes, almost never strategic mistakes. In fact, what me and my friend found was that quite often, surprisingly enough the people who beat us didn't even PLAY with a strategy in mind, by their own admission! They just played by the seat of their pants, looked for opportunities to capitalize on TACTICALLY, and won that way (wow, if I do this, and he does that, and I do this, I can fork his king and queen and take his queen!).
My strategy was almost always better than my opponent's in chess. My tactics were not always better. My friend and I discovered that, at least at the level of chess we were playing at (and I strongly suspect it is true of ALL levels of chess), "tactics dominates strategy." In other words, if you have better tactics than your opponent, but he has better strategy, you will win and he will lose.
My game improved the most, the fastest, the best, when I finally chucked strategic play and concentrated and boned up on tactics.
I think Sins, the way it is played online multiplayer, is like this. However, I will grant you that SP can play out however you like.