You seem to be interpreting the T&Cs as meaning that each group of three different brands - with no duplications during the promo period - would qualify for an additional 3000 bonus points. Therefore (Four Points + Courtyard + Aloft = 3000 points) followed by (Sheraton + Marriott + Westin = 3000 points) followed by (W + Element + Moxy = 3000 points) to make 9000 points in total. I read it that there's one additional 3000 bonus points awarded during the entire promo period after three different brands.

Anyone any thoughts on this?

EDIT: You may be correct now I've read more of the promotional stuff. Keeping the maths simple, this means there's about (30/3 * 3000 =) 30,000 additional bonus points if anyone goes out of their way to stay at all the Marriott brands.