Personally, I wouldn't go through any tunnel without good taillights and a decent amount of reflector tape on my bike. The tunnel warning light is a nice idea, but it only works if passing motorists read and understand the signs. Even if a motorist reads the sign and is looking out for cyclists, making yourself a little more visible will make it easier for a motorist to see and avoid you safely.
I won't tour without lights any more, and I have a taillight permanently mounted on my road bike for tunnels, bad weather, and rides where I might come home late. I add a headlight (Cateye EL-530) if I expect to be out after sunset.