I've been giving this a lot of thought recently, and I have to say, I think it would be really cool if the Nancy Drew games tried something risky again.
Before you all start coming out at me with pitch forks, hear me out.

I think it would be really cool if we got a 2.5D side scrolling, platform-esque Nancy Drew game that still became first person point and click when we need to.

What are the differences between a first person Nancy Drew and a 2.5D Side Scrolling Nancy Dre experience?

This game is catered to the young adult Nancy Drew audience. So it's already for adults.

1. We see Nancy. We see her face, her facial reactions to situations, her determination, her spirit, her frustration, her perplexing, etc. The player controls Nancy Drew in a side scrolling enviroment. Take for example, Nancy's bedroom. The player can use the analog stick to make Nancy walk/run left or right around the room. Nancy can jump or crouch. When Nancy collides with a hotspot, the game switches to a first person prospective, allowing Nancy to investigate objects or puzzles of interest in the 1st person prospective.
Nancy can also hold and use items while in both prospectives. For example, in the side scrolling view, Nancy can equip a flashlight to shine on dark areas like passageways, or use the analog stick to shine specific areas of a room. Nancy can also equip various objects to use at her disposal like keys, lock picks, maybe even add a combat mechanic and have Nancy take down enemies with weapons. She can heal with koko kringles and purchase them in vending machines.

2. Cutscenes and dialogue are more fluid in the 2.5D side scrolling prospective. Look at a game like Oxenfree or Afterparty from Night School Studio. That's the vision I have for a Nancy Drew title. Multiple characters can be on the screen at once, and Nancy can choose between a variety of dialogue options that may or may not contribute to the conversation. Nancy can walk and talk with characters. She can run with characters, climb stairs with them, help them if they fall, etc. There's a lot of flexibility here for dynamic cutscenes.

3. Puzzles can be a mixture of first person and platforming. There's no end to the potential and creativity when it comes to the types of puzzles we could get from a 2.5D side scrolling/first person Nancy Drew game. It adds a whole new layer of puzzle solving.

4. The game would be more accessible for consoles since players can use contollers in a much easier way with a game like this than for a 100% first person point and click game.

There you have it.
A spin off Nancy Drew title that if done right, could really be a great experience.
For a better example, I recommend you check out Oxenfree or Afterparty.
My vision is basically those games, but more zoomed in.