Metal-oxide valence-change memristive devices are the key contenders for the development of multilevel nonvolatile analog memories and neuromorphic computing architectures. Reliable low energy performance and tunability of nonlinear resistive switching dynamics are essential to streamline the high-density circuit level integration of these devices. Here, manipulation of room temperature-synthesized defect chemistry is employed to enhance and tune the switching characteristics of high-performance amorphous SrTiO3 (a-STO) memristors. Substitutional donor (Nb) doping with low concentrations in the a-STO oxide structure allows extensive improvements in energy requirements, stability, and controllability of the memristive performance, as well as field-dependent multistate resistive switching. Evidence is presented that room temperature donor doping results in a modified insulator oxide where dislocation sites act as charge carrier modulators for low energy and multilevel operation. Finally, the performance of donor-doped a-STO-based memristive nanodevices is showcased, with the possibility of mechanical modulation of the nonlinear memristive characteristics of these devices demonstrated. These results highlight the potential of donor-doped a-STO nanodevices for high-density integration as analog memories and multifunctional alternative logic elements.