MaxisMC: There are some known balance issues with the casino specialization that are being investigated. Improving your city's tourist attraction by adding landmarks and mass transit will help. It is possible to get the HQ, and focusing on one casino might help, but it is a lot more difficult than intended.
Looks like there was a last minute adjustment of non-basic casinos that adjusted their profitability that is being reviewed by Maxis.
In my last casino city I did have (2x basic casinos) and a sci-fi casino going at roughly breakeven with one disco and 2x hotel low wealth rooms. With this setup I was maxing out on low wealth patrons but only a smattering of mid-wealth patrons. (Oh and I did have Toyko tower to bring in the tourists).
I would suggest:
- better mass transit: train station in the downtown 'core', boats w/ cruise ship upgrade, airport
- spam basic casinos to get the lodging upgrade at the HQ before moving onto the top 3 casino types
The sci-fi casino has much higher running costs so you need the money that is made from mid-wealth tourists, not low-wealth ones.
With the smaller city sizes the game is much more about "leveling" ie: build/max out our city at one income level, making a tweak (HQ upgrade) and then going back and upgrading buildings. Only time you can short circuit this is if someone else in your region already has those buildings.