I personally don't think they actually do much good directly. They passed in all 11 states. The threat is that either state courts or federal court use the "Full Faith and Credit" clause to shoehorn in a national requirement. These measures, even the state constitutional amendments, won't stop sufficiently determined judges.

Such judges are not only willing to ignore the law to achieve their ends, they have also shown utter contempt for even overwhelming popular opposition to their social engineering. David Frum chronicles in detail how courts in Boston, and indeed, nationally, ignored popular, bi-racial majorities of 80-90% opposing busing.

The value of these referenda isn't that they establish any law that courts can't overturn. The value is that they place front-and-center, in terms most people can understand, the importance of judges, and the importance of appointing judges who respect the law, rather than making it up as they go along.

UPDATE: Listening to Hugh's show. I say it here. John Eastman says it there five minutes later. At least I'm in good company.