FIRST think of taking it only one time; after you've taken it and seen your results, THEN think about taking it the second time.
And no, I've heard that every test will be different and you never know what questions you'll get, so it could be easier or harder.....
I see that you edited your post. Sure, with SO many tests being administered it is probable that ADA recycles the questions. BUT, the chances of you getting the exact same questions? I'd say ~0%.