As a dungeon designer expanding the dungeon step by step to attract heroes to come and balancing the benefits and puzzles to make them enjoy my dungeon more is a very good idea!
Our team came up with a very similar idea in the beginning, but in the implementation, we accidentally got a "very stupid wandering ghost" due to AI design issues, which made our game more like the player guiding a timid ghost not to stop staying in the dungeon due to excessive fear. (Feel free to try our version if you're interested :) )
It's nice to see someone else pull off a similar idea, and good ideas should be experienced by more people!