  We study the degree of entanglement of arbitrary superpositions of $m,n$
photon-added coherent states (PACS) $|\psi\rangle \propto u |{\alpha},m\rangle
|{\beta},n \rangle+ v |{\beta},n\rangle |{\alpha},m\rangle$ using the
concurrence, and obtain the general conditions for maximal entanglement. We
show that photon addition process can be identified as an entanglement enhancer
operation for superpositions of coherent states (SCS). Specifically for the
known bipartite positive SCS: $|\psi\rangle \propto |\alpha\rangle_a
|-\alpha\rangle_b + |-\alpha\rangle_a |\alpha\rangle_b $ whose entanglement
tends to zero for $\alpha \to 0$, can be maximal if al least one photon is
added in a subsystem. A full family of maximally entangled PACS is also
presented. We also analyzed the decoherence effects in the entangled PACS
induced by a simple depolarizing channel. We find that robustness against
depolarization is increased by adding photons to the coherent states of the
superposition. We obtain the dependence of the critical depolarization
$p_{\text{crit}}$ for null entanglement as a function of $m,n, \alpha$ and
$\beta $.
