This is excellent advice. Thank you for taking the time to post.
I do still wonder if there is a tourism bug, because I have 2 gambling houses that were making great money. I made no major changes to the city, and out of nowhere, within the span of a minute, both casinos went into the red and dropped nearly all of their visitors. When I queried the wave of regional tourists who were headed back to my regional bus depot, they all said, "There are no hotels here, I'm leaving". I have empty hotels in BOTH of my casinos and some big ones in my commercial areas saying business is just 'ok'. There was no major change to the city wealth, traffic, or utilities when this happened. I have a 100k population, loads of low/medium wealth residents and only low/medium add-ons to the gambling halls.
Can you think of any other reason this might have happened?