Thanks Detailer, Graeme, and Brian for the thoughts and insight. I'm leaning toward just staying with Cypress Harbour....my only hesitation is better water action at Harbour Lake for my 3 yr old son, but I'm thinking he will love the pool at Cypress just fine, and the main attraction for him is going to be all of his Mickey, Toy Story, Nemo friends, etc., anyway. Plus, we might just go to one of the water parks for a day and I'm sure that would make up for any water area difference which might exist between Cypress Harbour and Harbour Lake.
I'm also seeing that the rental car is probably a necessity when staying offsite. And I do like the flexibility it will provide, and with a 3 yr old and 1 yr old, we will need flexibility. In fact, while I've always felt spoiled by the onsite bussing, now that I'm thinking about it more, I think there's an advantage in being able to throw my 3 yr old in a rental car rather than keeping him occupied at a resort bus stop. While the onsite resorts drop you off right in front of the parks, the travel time difference might not be all that different considering the rental car takes the waiting at the bus stops out of the equation.
And finally, while I have you here, here's another offsite question: is the ADR restaurant reservation system available to offsite guests, or is that only available to onsite guests?
Thanks again for your help.