Differential spatial modulation (DSM) is a noncoherent multi-antenna technique that conveys additional information by selecting transmit antennas. Space-time block coded DSM (STBC-DSM) combines DSM with STBC to achieve a transmit diversity order of two. Recently, we proposed a new STBC-DSM scheme that improves spectral efficiency through temporal permutations, termed bandwidth-efficient generalized DSM (BE-GDSM). This paper enhances BE-GDSM in two key aspects: either reducing detection complexity or increasing spectral efficiency. We propose a maximum-likelihood (ML) detector with significantly lower computational complexity for BE-GDSM. Besides, we introduce spatial permutations for STBC-DSM and demonstrate that such permutations require differential encoding. Building on this observation, we propose STBC-DSM with joint spatial and temporal permutations (STBC-DSM-JSTP), which achieves the maximal number of antenna bits among all STBC-DSM schemes. Numerical results show that STBC-DSM-JSTP improves error performance compared with BE-GDSM at the same data rate.