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The final word from CA franchise tax board on it:

You cannot deduct Mello-Roos taxes if they are assessed to fund local benefits and improvements that tend to increase the value of your property.

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Right now and in future property values will not increase (may decrease) at least next 3 or 4 years (based on 2006 prices).
I heard Mello-roos money used for building schools, libraries and public parks too. These facilities are not for just those with communities Mello-roos.
I believe tax code is not clear enough to say “Mello-roos is not tax deductible”