Thank you, I appreciate your taking time for this.
Actually, I find using a null-size raycast under the cursor very useful. It provides a lot of very easy to access information. It's not a technique I've seen elsewhere but I guess there are better ways of doing it. I'll certainly check out what you suggest, in particular Control nodes.
I realise that raycast can't help with depth but I'm still looking for the tool that would mimic human perception. Even in a flatland world, there are still sprites "on top" of each other. I want to be able to pick that up, in the same way as a person playing a game would expect to be able to pick the sprite up with a drag gesture. It's a sort of 3d world represented in 2D, much as playing cards are in many games.
Back to the drawing board but seriously - thank you again.