Near most MTR stations, there will be any number of noodle houses that will get you a satisfying and tasty dinner of noodles or rice plus roasted meats or fish/meat balls for 35-45 HKD, a bit less if you go farther afield (e.g. Sham Shui Po and Tsuen Wan). I was in Wan Chai and places like that abounded for 35 HKD. That can be your "cheap" night.

For splurging, maybe try an interesting place instead of glamourous high-end?

One memorable place that didn't turn out super expensive because we were light eaters was Jumbo Floating restaurant. Literally on its own mini island such that everyone, including employees, needs to sail in on a small ferry (a very short ride). Very colourful picture-taking at night. 4 of us cost less than 700 HKD.

If you want cheap Michelin star, then, again, in Wan Chai, there's Congee King at 7 Heard St. A bowl of congee set me back like 45 HKD and it was superior to others I've had. But because it has its Michelin star, the waiters are in uniform and they feel they can tack on the 15% gratuity that higher-end places in HK charge but which I've never seen at any regular noodle/congee house.