Hey, these look pretty good but just to give you some additional ideas it won't hurt to look at how some others have done it.

This guy uses a slightly distorted view and to me pulls it off quite nicely. Combined with the lighting effect I think it could be something you want to look at: Henning and here is a link to what I'm talking about.

I think it mainly comes down to sharpness, lighting and shadows and by that I mean if I was trying for it, I would make the highest items crystal clear and the lower items gradually softer and then combine light and shadows to further the illusion.

Also, I think these are looking great!