The cables aren't meant to be left up there all year long. They should come down in the spring and go up in late fall.
They aren't hard to put up and are very inexpensive. Especially compared to cutting in a roof vent or adding soffit vents that might not work anyway.
I have had major ice damn problems this winter and so have many of my neighbors. Venting the roof of adding insulation won't guarantee that they won't form.
The best protection that I have found is the the heated wires you lay on the roof and in the gutter. Unfortunately, I didn't put them up...