I'll go ahead and post my thoughts here, since the other thread blew up to quickly.
In my view, on balance balance is desirable provided it itself is balanced.
Fundamentally, balance isn't a game problem; it's a people problem. With the right group, you can play the world's most unbalanced game -- Rifts, for example -- and any balance or lack thereof built into the game system simply would not matter, because the group could handle it.
On the other hand, it just takes one player who has different expectations than the rest of the group, an an imbalance will just break the group. I'll give two examples. I DM'd a campaign where I had to restrict access to certain materials for the whole group because I had one player who I knew would abuse that material. Talking about it with him didn't stop the behavior; he just had different expectations (and it wasn't the sort of thing you'd lick a friend out of the group for) -- so we worked around the problem by imposing balance on the game system. I was a player in a different group where one of our players would use charop board suggestions to design his characters, where everyone else was focused more on fun and less on optimization. It became a significant problem by the time we'd advanced into mid levels, and the DM ended up having to take drastic action.
In neither of those examples is the issue fundamentally a game design issue. However, better game design could have reduced the pain. Good game design should try to minimize the amount of judgment the GM must impose in balancing the game -- the game should not require absolute rules mastery to manipulate it so that it works for your group. So I'm a fan of game designs that build in some relative balance, and do so in a way that works out in play -- no balancing via flavor elements or metagame concepts like XP. But no game should go so overboard in pursuit of balance that the playability and pursuit of fun is lost. Not everything in a game should be equal, but it should be fair to all players. Reasonable balance is the goal, not perfect balance.
So balance, in the end, must be balanced with all of the other elements of game play ... but it should be present in some amount.