I used to think that game balance was the ultimate goal in good game design. While working with Richard Garfield and Skaff Elias on a game that will probably never see the light of day, they persuaded me otherwise.
For one thing, it's nearly impossible to perfectly balance a game. Unless you have a trivial game like rock-paper-scissors, if you have a game with interesting nonlinear interactions some strategies are going to be better than others.
For another thing, if you do balance perfectly, and all strategies are therefore equally good, what exactly does the player have to learn? How can they show their skill? How can they feel that sense of accomplishment that comes from getting better at your game? Although in an unbalanced game, players will eventually find the best exploit and get bored, in that theoretically perfectly balanced game, there's nothing to find.
You see this in Magic: The Gathering. Some cards are strictly better than other cards. Some decks are strictly better than other decks. Learning MtG is partly the process of learning the values of different cards, and learning how to build decks.
An interesting part of Magic history I heard from Skaff - I forget which release it was, but one season they accidentally created an exploit where there was essentially a single best deck. Magic sales jumped that season. Why? They're not sure - one theory was that suddenly players knew how much they really had to spend to play Magic, and it was a reasonable amount. (Around $50, IIRC?) So they didn't rush out a fix or a rules change to cure the exploit, they rode it out.
I'm not saying don't balance at all. I'm saying do your best, accept that you won't make it, and then go ahead and ship that unbalanced game, with its various exploits and worthless units. And after a while, ship an update, with new exploits and new worthless units. Keep things fresh that way - and gives your players something to talk about.
It's a fine line between 'exploit' and 'that's just how you're supposed to play.'
Anyhow, that's what I've come to believe. What do you think?