The style of wall that I have made is in the default art...I have variations on this never released, but you will get the idea. I don't know about Dinonykos, but I have only used walls that goes up/down one floor at a time. I don't think it would be terribly difficult to go up two or more floors, but it depends on how you envision the stairwell.
Dinonykos, I love your sketch. I would play that design and be dazzled by the artwork.
Totally not what I imagined, however. I pictured open stairs, leading to open platforms with diverging side paths (that may or may not be stairs). If you have read the Robert Jordan "Wheel of Time" series, I am picturing some like The Ways. Or conversely, something omore akin to an MC Escher painting.
How to do epic art? For something like this, with open or closed or whatever stairs, I think it is about Depth of Field. You Up Close and Near By walls are crisp and fairly well lit, but your Far Away walls are darker, less detailed (ehich happens anyway), and then you use backdrops to sho the area beyond as darker and less detailed yet. You could also do something with color scheme - the lower you go, more red the backdrops, or seomthing like that.
Now for me, I would also change the viewport. I think it is well known that I do not like th edefault viewport, but for this I might consider not using the square, but a viewport that is wider than it is tall. Or if you don't want to do that, consider using a lot of small pics and sprites that extend outside of the frame with the occasional big pic. You could also have "viewing platforms" with a spot to look down and images that show the stairs going down into the depths, etc.