Actually, I'd strongly recommend getting the copy of the dismissal. Unless you get the charge expunged or sealed (might not even be possible, even if it can be you might have to wait several years first) its going to show up on your criminal background check. Also, depending on the quality of the background check it might not show the disposition, meaning that a potential employer might wonder if the charge is still pending or resulted in conviction. You really need the dismissal to prove that it was dismissed.
You never know, you might move and need it one day and it might be problematic getting them to fish it out of a warehouse somewhere and mail it to another state. Get it now when its easy.