» those thousand words ♥
After 3 or so boosts it would be a different story though....
I'll be honest: I'm not personally fond of using DD on Pokemon that have less than like, 80 speed. One has to realize that Aggron has base 50 speed, so 1 DD would bring it to about 75 base speed, and another to bring it around the realm of 112. Which isn't too shabby, so to speak, except...who's going to let it set up that much? Having a weakness to the most common attacks in the game (and no way to really compensate for said weaknesses), it seems that Aggron is doomed where it is.
If it were to get a mega-evolution, then I'd hope that it would sacrifice either it's Steel or Rock typing for something more practical (though I'd prefer it to keep it's Rock typing if its type does change, for the sake of the 50% spdef boosts in Sand).