Let me show you what is happening that causes the vibration.
Here is a pic of the CV bucket and the "spider" (the set of 3 roller bearings that go in the CV bucket).
When the car is new the spider rides on a smooth surface in the CV. But as time goes on it makes a wear spot. This starts to happen by around 20k miles or so (this is very rough estimate based on folks who have complained about the vibration after lowering). The pic below shows what the wear spot looks like:
When you lower the car, it moves the spider to a new spot where it normally rides. Based on the geometry, the new spot is very close to the old spot. The vibration is caused by the spider sliding over the edge of the new spot into the old spot. It trammels back and forth there.
A spacer takes care of the vibration by moving the spider far enough away from the old wear spot so it can't trammel into the old spot. Swapping the cv buckets from right to left and vis versa fixes the vibration by giving the spider a new surface to create a new wear spot.
This is also why ap2 drivers didn't think they needed spacers. It wasn't until the ap1 was a few years old that they would have a wear spot and when owners lowered the cars after they had 20k+ miles on them they got the vibration. At that time the ap2 was brand new...and they didn't have wear spots yet.
Now, older ap2s have wear spots too and can get the vibration for the same reason the older ap1s did.
Is a spacer better than swapping the cv buckets? It depends on your mechanical skill and wallet. Swapping cv buckets is free, but does take time...you have to pull the axles. The 2-piece style spacers can save time and are easy to install, but they are $175-200. The 1-piece style are useless as they take about as much time to install as it does to swap the cv buckets.

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