flash for WDW trip - SB-400 ok?

Last time I went to Disney world, I quickly realized that I needed more flash power. I assume it would help me drop my camera's ISO for indoor shots. But more importantly, I took enough pictures outside to realize that fill flash would go a long long way to evening out the shadows in the daytime pictures I took around the parks.

I have another trip there planned for November, and I'm wondering if an SB-400 will make a noticeable improvement in my pictures. Is this flash powerful enough to fill in facial shadows, outdoors in the Florida sun, at 10'-20' ?

I'm not looking for professional results, but I'd like to see a significant improvement from my D3000's onboard flash.

Thanks