Mate, Im not too sure what would produce better fuel economy. If everything is checking out fine I would look at your driving styles, the right foot controls most of your economy.
Blocked injectors I would think you would have worse trouble then bad economy - but it is plausable.
Small things produce better economy as in good quality engine oil, clean air filters, pumped up tires, quality fuel, IAC working properly (your car adjusts idle as it warms up?).
Im not to sure on what kind of memory capability the skyline has, but maybe its worth erasing that by undoing the battery and pushing the brake pedal. Should reset a few values the car "learns" about different throttle and load positions.
Cheers
Sumo