I have this mesh:
As you can see, the faces are triangulated. I want to know if there is a way to re-polygonize the entire mesh (make use of NGon support in Blender 2.63+), or a modifier or something else
Assuming you have no way to access the original (non-triangulated mesh), there's no way to get the exact polygons back, which may have existed at some point in some other application. But you can try several things in Blender, to get some polygons from any triangulated or tessellated model.
You can try the Limited Dissolve operator (X), which removes less important geometry using an angle to determine the importance (a subdivided plane will turn into a single quad using an minimal angle of 0.001°, since it's flat).
There's also a modifier, that acts the same, but non-destructive: Decimate set to Planar.
Less automated, but potentially better results are achievable with Dissolve Edges. Switch to edge select mode, select the edges you wanna get rid of and execute the operator (X).
You can also select multiple triangles and try to join them using Make Edge/Face (F).
You could also try using Tris To Quads. Access in edit-mode from the menu:
Mesh -> Faces -> Tris to Quad or by pressing Alt-J.
The Remesh modifier will completely redo the mesh, but it destroys your UV maps, and the kind of mesh you get out of it might not suit this kind of mechanical object. It also requires either loosing detail, or increasing mesh density. After remeshing you could try decimating or manually deleting excess edge loops.
The best quality solution is to remesh your figure manually. It's also the slowest option.