Sometimes, when I've visited the hotel (or any other pay-as-you-enter rooms in Adventure), I accidentally or mistakenly click the Return button after paying.
This has happened in the Grand Hotel in Pixpet City, for instance, when after looking under the bed I pushed "Return" only to find myself back in the lobby, where I have to pay for another room since I had accidentally left.

I feel that a simple prompt saying "Are you sure you want to leave without sleeping?", making it accessible once paid for the duration of the night, or even just not letting the player leave until they sleep would help to avoid this.

I'm not sure if this is just a me thing, or if anyone else also faces it, but I think it might be a nice little feature.
Hope this suggestion sounds interesting to you!