Mirror slap: highly overrated?

Mirror slap is the effect in DSLR camera's where the image loses sharpness due to camera movement induced by the miror flipping up.
I tried to do some tests on the Nikon EM, which is supposed to have really bad mirror slap. I mounted the camera on a tripod, attached a 300mm telelens and took 3 consecutive pictures: one without mirror lockup, one with mirror lockup (accomplished on the Nikon EM by using the self-timer) and one with a  modified mirror bumper.

Let me explain you the modified mirror bumper. When the mirror moves out of the way for the picture to be taken, it needs to stop at some point. The transition from the mirror being in movement to the miror being halted when it is folded against the groundglass is only possible when it decelerates. The deceleration creates a force (momentum) which will be counteracted by an acceleration of the camera in the opposite direction. This is what is inducing camera shake.
To minimise camera shake, we need to minimise the deceleration force on the mirror. To this end, a foam bumper is mounted at the top of the groundglass. The idea is that it will bring the mirror progressively to a halt. My modifified mirror bumper is a mirror bumper of double tickness, but modified in the form of a sawtooth. This causes the deceleration to start earlier with the resistance of the foam progressively increasing. The end result should be (theoretically) that the acceleration force the camera will be subjected to will be a lot less (about half).

The theory is nice, but the test results are not convincing: the 3 images (left: normal mirror slap, center: no mirror slap due to mirror lockup, right: reduced mirror slap with modified mirror bumper) show no difference whatsoever (check for yourself: the image inserted in this post is a 4800dpi enlargement of the center of the 3 negatives). Either this means my test was not valid and I need a sharper film, lens or scanner. Or it could be that mirror slap is highly overrated. Note that I tested for the worst possible conditions: light camera, heavily bouncing mirror, long telelens and a shutter speed of 1/15s to maximise mirror slap.
I think many people overrate mirror slap because of the camera shake they feel in their hands. Most of this camera shake is not having an effect on the image, since it occurs when the mirror flips back into it's resting position (where there is no foam to dampen the bouncing). Since the shutter curtain is already closed at this point, it is not influencing the picture.

A second, less scientific test I did was comparing my Nikon EM (light camera, bouncy mirror) with my Nikon F-301 (heavy camera, smooth mirror) for handheld available light shooting. In this case, I definitely had more sharp shots on 1/15th and even sometimes 1/8th when bracing myself with the F-301 than with the EM. But this can also be because the size and weight of the larger camera make it easier to hold it still, without miror slap having anything to do with it.