As my father is Spanish, we have spent our lives carrying papers and are very use to having our vehicles searched every time we cross the border. A CA driver's license was never enough, so my mom always carried our birth certificates when we were younger. Now, they carry passports, especially when they go to Arizona every year and then into Mexico.
My father and younger brother were the only ones who looked "Mexican" (the rest of us were lighter), but we were all checked. I think it was mostly because my father didn't speak English well and now it is because he still has an accent.
It didn't bother us, as we always planned for the extra time needed and always knew we would be searched. It was just normal, as we grew up with it. I guess this is why I am more patient when going though airports and while traveling in other countries.
