As a kiwi currently living in Vancouver, Canada my reasons for holidaying state side are simple:

1. proximity,
2. the mrs is a yank...

But most of my holidays down there are for hiking. Am off to do the john muir trail in two weeks, have done a lot of hiking around hte national parks of the west. Yosemite, Yellowstone, Grand Tetons, Grand/Bryce/Zion/Canyonlands/Arches/Natural Bridges hell I love UTAH!

Otherwise it's a massively vast country with a lot to offer - but as the OP said, it's a massive world. Dont spend all your time in one place. For culture, go to San Miguel De Allende in MX. Awesome!