What happens if I re-apply a stain?
Stain never "dries" the way a lacquer or poly finish does.  It will cease to be "wet" after awhile, but it will still just come off on your hands and clothing etc.  Not a good idea to just leave it on there.

Ultimately it is only darker if more of it soaks in.  Reapplication after wiping will darken it only slightly, as most of the wood pores are already saturated.

The darkness achieved by staining wood is effected somewhat by how much you use, but more by the color of the stain and the absorption qualities of a particular wood.

If you want your project darker, I suggest you sand it down (to get fresh wood that can absorb new stain) and apply a darker stain.