Not speaking from experience here because I don't own any down products yet, but I believe the main attraction to down is weight and compressed volume, and the fact that it's so soft and fluffy. Another pro is that if taken care of properly down will also outlast synthetics.
Really the only pro to synthetic insulation is that it will still insulate when when.
If you take care of your gear when out, the only thing that should get wet is your waterproofs and tarp. Dwr coating on shells will repel any small accidents.
If the dri down is as good as advertised it will be well worth the investment in my opinion.