Visually they are very similar but to the trained eyes, they can tell the difference.
The slight differences are, in addition to what's been listed above in the thread:
Base Model R34 GTR vs V-Spec:
- Had a firmer suspension = Lower ground clearance (But still sits quite high)
- Front and Rear Carbon Fiber Diffusers.
V-Spec vs V-Spec II:
- Equipped same to the V-Spec but:
- Had an even more firmer suspension = More lower ground clearance (But still sits quite high)
- Carbon Fiber Bonnet with NACA Duct
- Larger in diametre in rear brake rotors.
Interior trims slightly varied from all three models along with the MFD.
Base Model had 7 different readings and the V-Spec / V-Spec II have 2 extra readings of Intake and Exhaust Temp readings.
Base model R34 GTR came with the ATTESA E-TS.
V-Spec / V-Spec II came with the ATTESA E-TS Pro System: It acts the same as the Base Model but has the capability to split the torque from left to right at the rear wheels.
The differences are subtle and not really worth the extra thousands of dollars if you plan on modifying the car.
Or you can just buy the Base Model and add on the carbon fiber parts later / upgrade brake rotors and suspension etc...