How do current spikes effect component lifetime?
Look into "thermal cycle". Presumably any current spike would result in additional (albeit transient) power loss in the motor. Inside the motor there will likely be junctions (solder junctions ?) in the winding. The solder junction would be slightly higher resistance, thus slightly higher loss than the surrounding wiring. This would result in a temperature rise at the solder junction (again probably small). However, a rise in temperature and subsequent drop in temperature is known as a "thermal cycle".  I have dealt with thermal cycling in substrate bonded semi-conductors where thermal cycling reduces the lifetime of the semiconductor by eventually tearing away of the bond.  

It may take several million extreme thermal cycles to disrupt or destroy equipment, but then  in an extreme environment, it might do well to at least consider thermal cycles.
    EDIT :  add link : http://nepp.nasa.gov/docuploads/99810235-C28A-4A8D-BD52223A33EF7CDF/ASME-Hawaii993-lockeed.pdf