The Lord of Time is "Quiet". Heh, heh...
Sorry... That's ironic...
Seriously, most of the Legendaries in the game are "trophy" pokemon that you catch for the sake of the story, not because you want to use them. If you want to use an uber-powerful pokemon, there are better ones coming up (Giratina comes to mind). If you want to try for a stronger Dialga, go right ahead, but you should seriously retry for a one-shot only if you are going to be serious about using it for something.
That's my two cents.