the unique example that i have found is to graph a complex function in 4D, but what about in higher dimensions ?
Well, 4D can also be used to represent quaternions. There are also octonians, which you can graph in 8D. These things are probably less useful than extra dimensions themselves.
You could use 5D to graph a function from the complex numbers to 3D, i.e. f : C -> R<sup>3</sup>. There's other functions you could try, which would give you manifolds of different dimensions.
There are plenty of applications in physics, like many particle systems, relativity, and string theory. However on the whole, 5D space is probably less useful than infinite dimensional space.
There is physics 'phase-space', which maps all possible coordinates into a sequence and maps, eg the state of a gas of N particles onto a single point in 3N dimensions.
I think that should be 6N. In phase space, you count velocity as a dimension.