Wrong, they understand the significance quite well. They know that it is a symbol of the city and the religion of Germany and Europe, and that if they burn it down they have a MASSIVE victory.
Unless the Germans start REALLY paying attention, that cathedral may not survive intact until 2017. Just like the WTC, they had a practice run, a probing attack, and the real attack will come later...the only question being "how much later?"
The French had better take good care of the NOTRE DAME cathedral.
Or have the French already given up?
Muslims will not hesitate to occupy the Cathedral/Dom. Remember when they occupied the Church of the Nativity in Jerusalem about 15 years ago? They overran the monks who were in charge of the edifice - jointly held by the RC Church/Franciscans and monks of the Greek (I think) Orthodox church.
I remember it well. They broke a lot of artifacts and defecated on the floors. By the time they left, the edifice needed to be scrubbed like it was a hospital filled with vermin.