A resort view is usually just a view of the Swan and Dolphin grounds or looking toward the Boardwalk. I think whether the upgrade is "worth it" is totally dependent on your travel style - we don't sit in the room and look out the window much, even when we've had a nice view, so it would not be worth anything extra to me, but you might use your room totally differently! If view is important, pay for the upgrade. Check back a few pages to see
@amalone1013's "amazing" rooftop view
In my experience, I would think it's unlikely that you will get a balcony room unless you've reserved one. If you google the Dolphin you can see that about half the rooms on the "arms" of the resort have balconies, but the rooms located on the "triangle" and the flat part against the resort don't have any balconies - the upgrade to a resort view is not likely to guarantee you a balcony because there just aren't that many and a balcony room is in its own category. Of course, there are plenty of reports in this thread of folks getting upgraded to a balcony room, so it probably depends on when you're traveling and who checks you in.