| They say a picture is worth a thousand words, but I think we are well over that convention at this point. :) So here's two more pictures I will use to further show you what is going on. But first, I will directly answer your points. You are saying that there is air in the VTC that is preventing the noise from occurring and that there may be differences in working resistances between the parts if they were not installed exactly as they came out.
1) They were installed exactly as they came out - I marked all of the parts to ensure this. 2) The seal around the piston helix and cam helix are not 100% and will by absolutely no means prevent air from bleeding through them. They also not not 100% prevent oil from bleeding through them either. Air will find even the smallest of leaks and when the oil pressure is applied to the mechanism, any air is going to be very quickly forced out of the piston chamber. Even if there were air in that chamber, it will not serve as any cushion whatsoever. When the VTC is disabled, the piston chamber is open to the crankcase with only a flow of oil running through the cam bore. Any pressure, or cushion, provided by the air or even oil is negligible - the piston is resting on those four stops and with a spring of considerable tension holding it seated. In fact, if there were any air in them, they would be MORE inclined to rattle than if they were completely filled with oil - oil is a thicker fluid which will provide VASTLY better cushioning effect between two flat plates being forced together. So your air cushion theory is completely out the window. What I see in your approach is exactly what possessed my mind in the first few hours after disassembling a VTC. They are complicated little buggers and I was quickly finding myself imagining testing devices that could be used to check all of these factors you are carrying on about. However, and what is very likely different in my experience than with yours, is that I machined the rear plate's o.d. so that it would simply slip into the main VTC housing without having to press it in. This one little thing is what led to me discovering the large amount of axial play in the thrust face, and then upon seeing the wear on the parts, it became pretty clear to me what was going on. I can only speculate on your experience with the VTC, but if you didn't machine that o.d. such that the plate would simply pop back into the housing, you wouldn't have see this slop I am talking about so easily. You would have had to press the back plate back into the housing with the cam helix being the only part installed in order to see the slop I am talking about. But again, I Am only speculating on your experience there. All I know is that the axial slop is what causes the rattle, and the rattle is the outer sprocket "ringing" when it slams back forward against the rear thrust face. Right now, when I go out to my car with that punch and apply pressure to my VTC sprockets with the engine running, there is no longer any jackhammer motion or any noise at all. It isn't like "well, it makes a little noise here and there, but it is a lot better"... NO, my VTCs make absolutely no noise at all, anytime. So, the friction of fitment from misplacement during reassembly - Negative. Some sort of "air cushioning" occuring - negative. Have you tried applying a bit of force to the VTC front cover plate with the engine running with your upgraded VTCs to see if they rattle or not? I can absolutely guarantee that if all you have done to the VTC's internally is put a stiffer spring in there, your upgraded VTCs will jackhammer when force is applied to the front cover plate, thereby proving to you that your mod is more of a band-aid rather than a true fix of the problem. What your mod is doing is causing the anti-lash mechanism of the piston helix to clamp even tighter into the housing helix and cam helix, thereby preventing the outer housing from jackhammering off the rear thrust face. This is going to cause more wear on the helical bits as the anti-lash mechanism bites even harder into the outer housing and cam helix teeth. So here are the pics: 
You can see clearly in the top picture that there is a small gap between the two piston helix gears. This is the gap that is produced in order for the teeth to properly align to both the cam helix and the sprocket helix. The stiffer rear spring you are using is pushing against the back of the piston helix, which is trying to force the two piston helix gears together, thereby causing the teeth to clamp even harder on both the cam helix and the outer body helix. This is what is preventing the outer sprocket from moving back towards the engine off the rear thrust bearing, and hence, why your mod will prevent the noise. However, you still haven't fixed the real issue, which is the wear produced on the rear thrust bearing. This can be easily proven by simply applying force to the front of your VTC sprocket and seeing the jackhammer effect I am talking about. But this increased clamping being created by the stiffer rear spring will cause those teeth to wear out quicker. I was mistaken originally in thinking that your stiffer rear spring would force the rear thrust faces together and cause more wear back there. I've actually spent more time figuring out why your mod works than I probably have put into making my mod, LOL. But this is the reason why your mod prevents the noise, but it isn't really addressing the real problem, and why the mod that I am doing works properly with a stock internal spring. It is simply the axial slop in the device causing the noise. The second picture shows you the axial slop in the rear thrust bearing. You can visually see the small gap between the back of the cam helix and the backplate (with the square drainback notch). When I tack welded that back plate, I held it securely in a vice and the backplate is totally against the stop in the main housing - this is an unmodified VTC I just cut apart to use to show what I Am talking about a little clearer. So, there it is.
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