INNER GROOVE DISTORTION

Ct, My question was a simple one, I thought.  You named the following as factors that impede the stylus: "tonearm setup, alignment [which is really the same thing], antiskate, condition of record".  A lot of this depends upon how you look at it, but I would say that tonearm setup/alignment, and antiskate do not impede the stylus, unless any of those factors was impossibly cockeyed. Of course, as you say, friction between stylus and groove is the major impediment and the root cause of the skating force, and probably groove tortuosity due to complexity of the encoded musical signal adds to the effect of friction. Plus dirt.

Ct, You wrote, ""anything" that is going to impede the stylus travel, be it tonearm setup, alignment, antiskate, condition of record - will be heard more readily at the end. Another challenge for the vinyl audiophiles."
Can you be more clear about what you wanted to say here? Because in some sense, none of the factors you list, maybe apart from dirt in the grooves, would be expected to impede stylus travel.  I believe the traditional meaning of the term "Inner Groove Distortion" refers to the fact that, as you mention, the LP has to crowd musical information into an increasingly shorter linear path, as the LP runs out of grooves. (Plus there is usually more tracking angle error on the innermost grooves, unless you're using Stevenson alignment.) There are analogies to this phenomenon in tape and digital reproduction as well.  Tape running at 15 ips and using half a track would be expected to provide much higher fidelity than the same tape running at 7.5 ips an using only one-quarter of a track, etc. And this is also why in theory 45 rpm sounds better than 33 rpm.  I'm sure you know this, which is why I wonder what you are saying above.

For what it's worth, the bearing type would have nothing to do with the magnitude of the skating force, all other things being equal, or of the amount of anti-skate needed to correct distortion due to the skating force.  It's merely that with a unipivot, excessive skating force would tend to pull the azimuth off.  Whereas, with a gimbal type, the headshell cannot roll around its longitudinal axis, thus there can be no effect on azimuth.
And finally, I still say that excessive skating force or excessive anti-skate would cause distortion most noticeable in one of two channels, not both at the same time, and would not exclusively affect inner grooves.  Such errors should be noticeable all across the LP surface, to varying degrees depending upon the magnitude of the skating force at any point.

I'm with millercarbon.  If the distortion is "global" (i.e., in both channels), then I doubt it's due to a lack of anti-skate per se.  Also, if you had a pronounced lack or excess of anti-skating force, you would hear the effect at the outer grooves as well as at the inner grooves. As millercarbon mentioned, too little anti-skate affects the R channel predominantly, and you would hear R channel distortion from the first second the needle hits the LP.  Too much anti-skate will do the same in the L channel.  My guess is that the movement of the tonearm is impeded by something (wiring, maybe?), as the tonearm travels toward the spindle.  That said, I do agree with others that the lack of any provision for anti-skate typical of older VPI tonearms is egregious. Check also to see whether the cue-ing device is fouling the arm wand, as the arm pivots toward the spindle.  Likewise for the counter-wt.