A multiconfiguration microscopic method has been applied with the Gogny effective interaction to the calculation of low-lying positive-parity states in even-even ${}^{26\ensuremath{-}32}$Si isotopes. The aim of the study is to compare the results of this approach with those of a standard method of generator coordinate method (GCM) type and to get insight into the predictive power of multiconfiguration methods employed with effective nucleon-nucleon force tailored to mean-field calculations. It is found that the multiconfiguration approach leads to an excellent description of the low-lying spectroscopy of ${}^{26}$Si, ${}^{28}$Si, and ${}^{32}$Si, but gives a systematic energy shift in ${}^{30}$Si. A careful analysis of this phenomenon shows that this discrepancy originates from too large proton-neutron matrix elements supplied by the Gogny interaction at the level of the approximate resolution of the multiparticle-multihole configuration mixing method done in the present study. These proton-neutron matrix elements enter in the definition of both single-particle orbital energies and coupling matrix elements. Finally, a statistical analysis of highly excited configurations in ${}^{28}$Si is performed, revealing exponential convergence in agreement with previous work in the context of the shell model approach. This latter result provides strong arguments toward an implicit treatment of highly excited configurations.