You can't really use DMM as an argument here though. A chameleon can't qualify for it without a dip in a turning class, at which point you'd probably be better off just using that class to begin with. With persistence out of the equation you've got arcane=divine at best.
After all, a chameleon doesn't have any more difficulty aquiring new spells for his book than a wizard does. The extra spell trick seems entirely unnecessary, especially since you have to have casting ability outside of chameleon to use it. It'd be useful if the DM was stingy about giving access to new spells, but he'd probably just nerf the trick out of existence in that case anyway.