We took our twin babies to Disney when they were 7 mos. old, 13 mos. old, and then 18 mos. old. Like you, we had also been to WDW many times before having children. Our last trip in November, when our girls were 18 mos. old, will be comparable to your situation. Let me tell you -- it was an awesome trip. Here are some pointers that worked for us:
> We took our comfortable stroller from home. That way, our girls were very familiar and comfortable in it and could easily nap during the afternoon right in the stroller. We recline the seats, put up the canopy, and they sleep for at least an hour. This is nice for people like us who are used to WDW without children because when they nap, we would have a nice sit-down lunch in Epcot (restaurants don't normally mind if you bring the stroller right to your table, especially if you are eating outside), so it's sort of still like a WDW trip without kids because you and your spouse can still enjoy a nice meal together.
> Go to the little children play areas in each park and let your son walk/run off some steam and get a little exercise.
> Make sure you have a plan for at night when your son will be ready for bedtime. Some nights, we let the girls fall asleep in the stroller and we watched some night shows and had a snack. Other nights, we put the girls to bed in the hotel room and then sit out on the balcony having a drink or snacks. Which leads me right into another suggestion. Get a room with a view. We never cared about our view pre-kids. But now we find ourselves in our room a lot more often, so it's nice to have something to look at other than the parking lot.
> Since you've been to WDW so many times, I don't need to tell you how convenient the monorail resorts are, but with a baby that fact becomes really important. You can just roll your stroller right on the monorail. For the bus transportation, you will have to fold up your stroller each time you get on a bus.
> You can take your son on any ride where there isn't a height restriction. We put our girls on our laps or in a baby bjorn carrier when they were smaller.
> At 17 mos old, your son will probably get a kick out of the character meals. Our girls did. He will be able to eat for free at buffets and character meals.
Hope this helps a little. I highly recommend taking your son to WDW at this age.
Debbie