Ah, so you've already got keep with previous? That was the main reason I
upgraded to CS6 from CS4! (Only half joking.)
Autosizing text frames is good for things like captions and
side-headings. But it's true that I do not use them a great deal.
Another reason to upgrade might be if there were a third-party script or
plugin that you need and is only available for a later version.