I went to the Cook Islands a few years ago around August (I think),anyway it was supposed to be best time for wind but as it turned out I ended up kiting once as the wind just never really came in the 8 days I was there. It didn't really bother me to much as we had a great time, especially at Aitutaki it's such a great place to chill out.
If I were you I'd take it anyway you just never know, it's such an awesome place to kite when it is blowing you'd be pissed off if you had no gear there.

Anyway have a great trip you'll have a ball.

Yes take it - I went in November when the wind was meant to be rubbish and kited 6 days out of 7.

Went in July when it was meant to be great and only got 2/8!

Aitutaki definitely the best kitesurfing

If your in aitutaki and in the off season wet and wild don't run their boat - instead go to the tourist info centre and ask them to get captain puna to do you a drop off / pick up - he was cheap and collected us as promised!!!