More Words, Deeper Hole

Spallation costs maybe 60 MeV of energy per neutron produced. And the best spallation sources are of fissionable materials, where most of the neutrons end up coming from secondary (subcritical) fission.

Spallation reactors might make sense for destroying higher transuranics (curium, etc.), which tend to have so few delayed neutrons when fissioned that you cannot operate a conventional reactor using them (far too much risk of going prompt supercritical -- BOOM). But if you're extracting and concentrating the transuranics for destruction, it's probably easier to just package them up and shoot them into space instead.

Fusors are fun toys, but cannot work as an energy source. Even as neutron sources, they really suck.