Also check out Jeff Thompson's work on voxels. He did some experiments using a CNC to build things out of spheres.
If you could come up with some kind of collet to hold the sphere, you could spin it like crazy and use friction welding. It may not have any advantages over spot welding, but some combination of spinning and zapping might work better than either alone. For example, spinning the sphere might help clean the surface of oxides and other junk at the points of contact, thus resulting in a much higher quality spot weld.
If you could come up with some kind of collet to hold the sphere, you could spin it like crazy and use friction welding. It may not have any advantages over spot welding, but some combination of spinning and zapping might work better than either alone. For example, spinning the sphere might help clean the surface of oxides and other junk at the points of contact, thus resulting in a much higher quality spot weld.