Monaco due to how compact it is, you can easily walk everywhere you need to go and spot cars while at it.
Dubai is a much larger place, like consider a scenario where you're at the Mall of the Emirates, you already went through the parking areas and want go to the next place, lets say the Dubai Marina,
thats a +30min trip on public transport.
In Monaco you'll walk 2 minutes from the Casino square to the next hotel or parking garage, 5 minutes to the harbor etc. You have a lot more time to actually spot cars.
You basically need a car in Dubai if you really wan't to check all the places.