Drawing charges is definitely more valuable than a block IMO, but a steal is debatable. Most blockers in today's NBA (Dwight Howard, etc) just block the ball out of bounds, which isn't particularly useful. A steal on the other hand often times leads to a fast break.
Of course, a block out of bounds is useful. It may not be as useful as tapping the ball to a team mate, but it puts your opponents in a situation where they have to in-bound the ball with less than a full shot clock. And, of course, a block means there no chance of the ball going in the hoop, so it's better than not blocking the shot.
Also, an attempt at taking a charge often yields a defensive foul. While that can happen on a block too, it tends to happen more in attempting to take a charger.
Furthermore, a shot blocker's defensive presence if often much more disruptive than someone looking to take a charge. A great shot blocker can make a player miss even when he doesn't block the shot. I'm not sure someone taking a charge can influence an opponent like that.
Well, if a guy is a notoriously good charge-taker, opponents will think twice about going into him and may opt for a jumper/floater instead of a higher-percentage layup.
And just because you are a good shot blocker doesn't necessarily mean you aren't susceptible to guards attacking you. They could be looking for a blocking call or contact in the air. Once a player leaves his feet he is dead meat. The NBA should look into guys jumping sideways into defenders solely looking for contact, but that's another story.