Three weeks is great. we usually go for three but this year had to cut back to 15 nights as our son, who is 17 tomorrow is on the 4 week NCS course which doesn't finishe till end of next week. have to keep reminding myself not to complain about 2 weeks as sounds so ungrateful.
You will get to book your fastpasses 60 days out instead of 30. Not sure how many days you can do this for if only staying a couple of days but theres plenty of info on the theme park boards. Theres a thread called Throwaway Rooms which has lot of info. people book a cheap room for one night to get the fP benefits.
Free parking of course, Magic hours. Its a lovely resort.
This year is the first time we have not been in Orlando on our sons birthday since 2010. I hope we will also be there on his 18th birthday next August. I dont even want to think about it coming close to last family trip there. I am not sure we could go without him. however, when I asked he did look at me and say, why wouldn't I go on a free holiday? So think i am safe for now.