If you're still wondering...
I've got the same holster for my Springfield XD9, and the wedge is for adjusting the camber, i.e. how far out the gun butt tilts away from your body. The extra bolts are not spares per se, but are slightly longer than the standard bolts that are installed at the factory, and are to be used if you install the cambering wedge.
There weren't any directions for this thing in my packaging, I just figured it out by myself. If you want the gun butt to angle out from your body, unbolt the holster from the paddle and install the wedge with the new bolts, thick side up. If you want the butt tighter in to your side, install the wedge thin side up. The curved hole allows you to make fine adjustments to the degree of camber by sliding it up and down, while pivoting around the bolt in the round hole; you can also vary the adjustment by installing the wedge with the curved hole towards the front, or towards the back.
Why use the wedge? Mostly, I think, for ladies with "hourglass" figures that actually cause the gun butt to slant inwards as the holster rides along the outside of their hip; they need to install the wedge so that they can get enough space between the gun butt and their side to allow the thumb in and attain a full firing grip when drawing the gun. You might also want the extra adjustment if you want to use the holster as a poor man's IPSC rig.
