The issue I have with Miles being spiked is who would know how to spike him? Sazed and Marsh are the only two that we know for sure could do it. Spiking people seems againist anything that Sazed would do. Marsh... what would be his motivation do something like that? It is possible that maybe the kandra knew about spiking, but they seem to be keeping a pretty low profile. Another issue with the spiking is that the spike had to be somewhere that could not easily be dislodged. With Miles tendency for getting blown up/shot this might be pretty hard to do without him noticing. Chances are, when he did notice, he would probably remove said spike since it would mess up the healing process.