The likelihood that the targeted companies hire you afterwards is VERY low. You basically just shat all over their baby.

On the other hand, other companies (who weren't shat on) will stand up and take notice.

Spec work is only when it's by request, and the request came from people who benefit from it (e.g. "show me how you'd do this before I pay you").

This isn't spec work, it's publicity-seeking. :)