Can't recall how low we went along Miami beach - it was pretty low but not 250' - wish I'd been sitting on the left or we'd been southbound, fabulous views. Later we passed some way behind a Citation on approach into Fort Lauderdale Exec which is around four miles inland - not sure how high we were but we descended to stay clear of his wake and still bloody hit it!
I would have imagined that the shoreline lights ought to give a good visual reference from a half mile (is that correct or is it a mile?) but not having flown at night in a light aircraft...