You're in WA - are you driving down? What time of year are you going (is the Siskyou going to possibly slow you down and delay your arrival?)?
If you're flying - is your ticket transferable? What's the fee? Or better yet, is it refundable at all?
Is this part of a package (I'm assuming) - would your hotel be refundable? Many times they take the first nights fee and refund you the rest - so how much per night would you be paying IF they have this policy.
I'm pretty sure your park tickets are non-refundable, but can you save them for a later date (when is the expiry)?
As far as sickness/health - that would be the biggest thing. We had the flu the week before we left and I was worried. Luckily we were better before we left.
I never take the insurance for our Disney
AAA packages. If I'm in the hospital then I'm not thinking about the thousands I've lost, if I'm not in the hospital, I'm going - even if I'm stuck in the hotel room.
Out of country trips (other than up to Canada since I'm a citizen and am covered), I get insurance not just for peace of mind but it's practical.