"I have five level 70s, therefore I'm good at the game!" This comment, or others that express a similar sentiment, is often heard in-game, on forums and here on WoW Insider.
Having multiple characters of different classes exposes you to many more facets of the game. An alt-o-holic, with multiple alts, enjoy a range of gameplay that is indisputably wider than someone who plays just one or two characters. While leveling content is largely the same, the classes are designed by Blizzard to be as different from each other as possible. Running through The Barrens on a Priest is a very different experience from running through the same zone with say, a Druid.
However, does sheer breadth of gameplay experience translate to a "better" player of WoW? Understanding how other classes work is definitely an advantage when you're playing in a group or raid, but is it fair to dismiss the "specialist" player who, through choice or simply lack of time, plays only a single toon?
In other words, does breadth of experience trump depth of knowledge as far as playing the game is concerned?