We investigated the influence of molecular parameters (amount of mesogen, cross-linking density, cross-linker length) on the complex shear modulus G* = G' + iG" of polydomain smectic-A side-chain liquid crystalline elastomers composed of side-chain polysiloxane cross-linked by aliphatic chains. G' presents two components in the isotropic phase. One is independent of the frequency and reflects the presence of the permanent network; the other is frequency-dependent and is characterized by a scaling law behavior G' = G" similar to f(0.5) of the Rouse type, where f is the frequency. We show that this scaling law is independent of the molecular parameters except when the amount of mesogen becomes very small. In contrast, the crossover frequency between the elastic and the Rouse regime is a function of the crosslinking density and the cross-linker length but is independent of the amount. of mesogen, except when the latter is very small. The elastic plateau follows the same behavior as the crossover frequency. It is no longer visible in the smectic-A phase, and the dynamics of this phase are essentially governed by a transient network characterized by a f(0.3) scaling law which is independent of the cross-linking density.