We went this past Spring Break. Cold, windy, and crowded. That said, the last time I was there was Spring Break 20 years ago and it was warmer (sweatshirts / shorts) with fewer people.
The weather can't be controlled, of course, but the hoards of people in April was shocking to me.
The kids still enjoyed it, even with the wind, and we did a bit of hiking. Lunch was a madhouse. We spent one day there and the rest of the week was spent seeing other sites along Rte. 66, Havasu, and Phoenix. Although I hate to say it, those days were all more enjoyable.