Matt,
I actually do peen that pin, although it's not strictly necessary. Glue and friction would serve just as well to keep the stabilizing spacer in place. In some instances, it would probably be better not to peen it, depending on the material you're using. Of the razors I have with a factory 3rd pin, one is peened (a Henckels), and the others aren't. I usually use a stainless steel standoff, rather than a plastic pin or bead. As far as them actually stabilizing anything, they do. They stiffen the handle quite a bit, and give a rest for the shank of the blade.