"I frequently encounter people who claim to be investigating "Celtic spirituality". By this they typically mean reconstructions of Druidry filtered through romantic legend."
Indeed there are. I have a cousin who is doing just that, though she's a bit of a loon! There are also "Celtic Orthodox" groups who claim to be Orthodox, but they are only a bit less loony than the Druid inspired crew!
It is good that you mentioned light in a dark world. That has always been my image of Iona and Lindisfarne and these two great saint/monks who approached God there.
Well, I always ask the neo-Druid loons when they're going to start up the human sacrifices again.