Hatta is an exclave to Dubai and even though you drive for over an hour and almost reach Oman it's still Dubai, with the dam clearly showing the leaders. You could also continue to Oman for another 10 minutes from here.

Most of the time you'll spend in the car to get here and then you should park to get on the free shuttle that takes you to the dam but in the late afternoon one can just drive up to see everything yourself. I saw the shuttle and it allows for better walking at the top so I would definitely recommend it in peak times. Nobody really mind that I was driving up there and stopped the car on a dam.

So while I enjoyed visiting Hatta, the water spots, see green in Dubai that wasn't imported water and feel you aren't in the Emirates anymore, I don't see it is worth a UNESCO status at all just for that. If you make a road trip into the area I would still recommend going. There is enough in the area to make it worth a visit.