OK, just to end the debate
...what I was saying that I couldn't find a burger joint or anything other than ice cream parlors on Lincoln Road
(this was 2006 btw), while our experience thus far in the US had been that there's always a place where you can eat in the US even at 2 AM.
The 11th Street Diner is (asuming it's on 11th Street) almost 1 km from Lincoln Road! I didn't wander that far. 1 km is the other side of town where I'm from!
Likewise "3 blocks north on 21st Street" is still 800 m in the opposite direction. That's also what I meant by everything being far apart and "medium walkable". These are at least twice the distances I'm used to and would consider walkable. South Beach is 4 km by 1,5 km, as a comparison central Amsterdam is 1,5 by 1 km.
Don't get me wrong, I really enjoyed South Beach and think it's an unique place with great urbanity, atmosphere and walkability. South Beach and Miami as a whole together with Washington DC are the top spots I wish we would have spend more time in.