Monolayers of transition metal dichalcogenides (TMDCs) have unique optoelectronic properties. Density functional theory allows only for a limited description of the electronic excitation energies in these systems, while a more advanced treatment within many-body perturbation theory employing the GW/BSE approximation is often rather time consuming. Here, we show that the recently developed LDA+GdW approach provides an efficient and at the same time reliable description of one-particle energies, as well as optical properties including bound excitons in TMDCs. For five exemplary materials (MoSe2, MoS2, WSe2, WS2, and ReSe2), we discuss the numerical convergence, in particular with respect to k-point sampling, and show that the GdW/BSE approximation gives results similar to common GW/BSE calculations. Such efficient approaches are essential to treat larger multilayer systems or defects.