I agree. He's part Hispanic and from the West. He'd balance a Hillary ticket.
Bill Richardson is closely tied with the Clinton gang. His selling point is his ability to bring in the Hispanic vote, which is not as overwhelmingly pro-Democrat as the black vote. Also, he should be able to carry his home state of New Mexico, a small prize to be sure (4 electoral votes), but lost by Kerry in 2004. As a Hispanic, he can help the ticket in the neighboring states of Colorado, Arizona, and Nevada, all of which are "light red", and perhaps Florida as well.