We booked the Inca Trail tour for the New Year's Eve of 2015 already in April 2014. Inca Trail Reservations came up as one of the most favored options after several hours of browsing. Now, after taking the hike, I do not regret the decision of going with Inca Trail Reservations.
Even though we went during the rain season we did not have too much rain (mainly only during day 2 when climbing up to 4200 m.a.s.l. at the Dead Woman's Pass). Rest of the time was a mix of sun, fog and beautiful miradors. The wide mixture of weather conditions did only add an extra dimensions to the tour, showing the lovely views and landscapes in all different possible ways.
I dare people to try to find a more valuable option than Inca Trail Reservations. Before booking, make sure that your physical condition is top notch, you are equipped with strong knees and not scared of early mornings. Gotta catch 'em all, Pikachu