Much cosmetic diversity on the Supreme Court has been created starting in the '60's with the first Black being appointed by LBJ, and then continuing with the women starting in the '80's. But where has this left us? If Kagan is confirmed, the Court will have 3 Jews and 6 Catholics, surely the most non-diverse Court in history! Also, they will all be heterosexual, another slap in the face at true diversity.
The real issue is whether any of this really matters. If you endorse the idea that the Supreme Court should make social policy, then of course it does matter. But if you believe that the Court should be interpreting the law and not making policy, then it doesn't matter.