Would a gimbaled, always horizontal cockpit be beneficial to fighter jets? Would it be possible to have a spherical cockpit that was gimbaled in jets such as fighters so the pilot was always upright. With all controls in the cockpit wirelessly communicating with the rest of the jet?

Wouldn't this be an advantage as it would be easier to aim and the pilot wouldn't get disorientated and could see anywhere by maneouvering?
With enough engineering (read, money), all sorts of things would be possible, but if you picture the aircraft in a hard, level turn, the g-forces would be pressing "down" relative to a conventional cockpit, but "sideways" for a cockpit that was gimbaled so the pilot was sitting upright relative to the horizon.  And that would probably be a lot harder to take than the usual "down" G-forces.  Resisting 9 G's pulling your hand and forearm straight down can be done with a support for your arm (side-stick controller) or a bit of a ledge at the bottom of the handgrip (side-stick or center stick), but keeping precise control of the aircraft with 9 G's pulling your hand sideways might be a lot harder.

Beyond that, the sideways G force would be pushing your head to the side, which probably ends up banging your helmet -- pretty hard sometimes -- against whatever restraint or canopy it meets.

Something that achieves some of the goals you mention is the "Virtual Reality" helmet of the F-35, where the pilot can essentially look through the airframe and "see" aircraft, targets, and whatnot even in places that he wouldn't have an actual line-of sight.  That allows him to look in any direction, reacting to threats, tracking his target, and so forth.  And without having to gimbal the cockpit.  Although for what the F-35's cost, that might actually be cheaper!