Reserving now gains nothing as you cannot even lock in today's rates. The one exception (which I assure you does not apply to any of us normal human beings who look for discounts) is for people who want the big suites (2 and 3 bedroom) at the GF. There are only a certain number of those and they are usually booked well in advance for paltry sums that begin somewhere around $1800 a night.
You seldom see any discounts being offered more than 6 months out and most pop up 2 to 4 months out. Moreover, if you are going to go the discount route just prepared to be flexible as you might hit a time when there are none at monorail resorts but plenty elsewhere. One thing to consider if you are set on a monorail resort is to make a regular reservation maybe 10 months out (a year if a holiday time) to assure you have one and then switch if a discount becomes avaialble.