Stayed at the Intercon as well. Nice hotel, as Ambassador member received a very nice upgrade. Taxis are cheap, not sure I would be planning on walking around much depending on time of year, UAE was extremely hot on our visit in August (43 degrees) and the locals said 'wait until we get the warm weather?". Views were fantastic from the Intercon lounge.
The city tour won't take up much of your time.
Ferrari world was a blast, yes the fastest roller coaster in the world and outdoors, it felt like you were in a fan forced oven. My wife has been on this rollercoaster and I can guarantee she has not seen it, eyes shut from the launch til the end, I was beaten around the face and upper body when we pulled up "I am not going on that beast ever again, you idiot".
An absolute must see is the Mosque, the scale, quality and architecture will blow you away. Our guide gave me a mujch greater understanding of their religion and why things are not as they appear to an outsider.