Do model species evolve away from Batesian mimics?
I have found some papers that support the hypothesis that an overabundance of Batesian mimics creates a condition for model species to evolve differentiating characteristics -- in particular,  Franks, D. W., G. D. Ruxton, et al. (2009). "Warning signals evolve to disengage Batesian mimics." Evolution 63(1): 256-267.

The authors argue that new conspicuous traits in unpalatable species evolve in response to mimicry, since a mimic that evolves conspicuousness without being a good-enough match pays full cost of conspicuousness without the benefit of its predator learning advantage.