I am in the same boat as you, going at the end of August. We haven't purchased the insurance yet, and I am leaning toward not doing it.
If there is a hurricane and the plane doesn't fly, they will put you on a different flight when it is safe.
We are traveling on AirTran, so if we just change our minds and decide not to take our trip, our non refundable tickets will cost an additional $75 each to rebook, or a total of $300.
If we cancel our package at DW close to arrival date, like the pp stated, we are out $200, but if we reschedule due to weather, I can't see DW sticking this to us.
So, for $140, I can pay for travel insurance to cover $500 in expenses
Net potential benefit = $360.
However, I am not taking into consideration lost luggage, because really, we can live in what we can carry-on, and we have plenty of clothes, so a few lost outfits are no biggie for us. I am also not taking into consideration someone getting sick, because we have very good health insurance that would cover us the same in FL as it would where we live.
If we did not have health insurance, or we had very expensive clothes, or we would not consider rescheduling our vacation to use our airline tickets (for an additional $300 versus forfeiting the entire cost), it would probably be worth it.