Why is it that some drawings show that cube thingy and other drawings dont? Well here is how to control both the “cube thingy” (ViewCube) and the Navigation Bar (NB) that sits just below the View Cube (VC).
The Navigation Bar and ViewCube also show up when a viewport is activated (double-clicked) in Paper Space.
To control the display of these tools in a View Port or in Model Space the method is the same. Just make sure that the the setting will only affect the current space (model or view port)
View tab > User Interface panel > User interface dropdown > Check or uncheck as needed
A possible configuration is to have the ViewCube be available in the Navigation Bar. This happens by default when you turn off the ViewCube. Notice in the picture below that the top button in the Navigation Bar is a toggle that quickly turns on the ViewCube.
The System Variable for these tools are shown below:
ViewCube System Variable = NAVVCUBDISPLAY
I don’t know how my current value is a negative one. Please notice however that this system variable is saved in the drawing. That is why it might be displayed in one drawing and not displayed in another.
Navigation Bar System Variable = NAVBARDISPLAY
Notice that this system variable is saved in your computer’s registry and will display the same (on or off) in any drawing you open.
AutoCAD Tips 
I have an issue with my view cube showing upside down (instead of showing in TOP it is showing in Bottom view), but when I bring in survey information or reference it to other files it is correct in how it should be showing. I just recently switched over to Civil 3D 2013 and am not sure if I am missing a hidden setting.
Try setting the USC to world and then aligning the “Plan” view to the UCS in world:
UCS
then
PLAN
i know this post is old, but i say this for future reference. Mine was showing back for the top view. Under the viewcube is a pulldown menu with unknown ucs selected, instead of WCS. Select that and it fixed it (at least for me)
good point! I sometimes forget to check that little box to see what UCS’s are in the drawing
~Greg
I’ve noticed that the Nav Bar randomly disappears while I’m drawing in model space. The fix I have found is to switch to a layout, then back to model space.
Good catch – I have also noticed weird things with both the navcube and navbar and the drawing controls (open, close, minimize) in the upper right corner of the drawing area. Especially when i am opening and closing many drawings, I have noticed this: open a draw, zoom extents, run the audit command, then save. when i go to close the drawing using the upper right drawing control (x), it isn’t visible until i zoom in or out… i can then click on it to close the drawing. Just an annoyance i guess. it seems as though a regen doesn’t even fix it. it takes an extra nudge to make it work
~Greg
The reason your “NAVVCUBEDISPLAY” was set to “-1” was because you were in Paper space.
I have an issue that my viewcube not showing in AutoCAD LT 2016, please send me the tips of the same.