Space-based gamma-ray and neutron detectors face strict constraints of mass, volume, and power, and must endure harsh operating environments. Scintillator materials have a long history of successful operation under these conditions, and new materials offer greatly improved performance in terms of efficiency, time response, and energy resolution. The use of scintillators in space remains constrained, however, by the mass, volume, and fragility of the associated light readout device, typically a vacuum photomultiplier tube (PMT). Recently developed silicon photomultipliers (SiPMs) offer gains and efficiencies similar to those of PMTs, but with greatly reduced mass and volume, high ruggedness, and no high-voltage requirements. We have therefore been investigating the use of SiPM readouts for scintillator gamma-ray and neutron detectors, with an emphasis on their suitability for space-based instruments for astrophysics and heliophysics. We present preliminary radiation hardness tests of two promising SiPM devices, and describe two concepts for SiPM-based instruments: an advanced scintillator-based Compton telescope, and a double-scatter neutron telescope suitable for measuring fast solar and magnetospheric neutrons. Supporting laboratory measurements are presented to demonstrate the feasibility of these telescope concepts.