I think sometimes we tend to underestimate the importance of the testimonies of the eleven witnesses particularly given how they refute so thoroughly many of the commonest objections levelled at the Book of Mormon. I remember that when I first read the Book the testimonies of the Three and the Eight made a great impression on me. Because of the way the publication was set out I came to them before reading either Joseph Smith's account or 1 Nephi. The facts that these events had been witnessed by so many others and testified to with such sincerity definitely helped prevent me simply discounting Joseph's story as a personal fantasy.
A short while after I was baptised I went through a bit of a wobble, thinking 'What have I let myself in for?' About this time the Stake President called me in for an interview (nothing sinister, just a welcome) and while I was waiting to see him I noticed a large picture of the plates being shown to the eight in the corridor outside the office. I remember thinking to myself 'Come on, this is true! They actually saw this!'
Much later I learned more about the individual histories of the witnesses and came across the testimonies you quote above. I think sometimes the passage of time can make it too easy to dismiss events we find inconvenient. Events that don't match up with currently held views of how the world works. Eye witness accounts and testimonies, particularly such forceful ones, enable these people to speak to us 'from the dust', and remind us that they were there and they know what they saw and no ammount of 21st century rationalising can change that.
Drew