First, I would be really upset if I planned on the Poly & my DH downgraded us to a value because HE got me preggie! (which my Dh has done 3 times )
As long as your wife is still up for it I wouldn't mess w/ my ressies. She probably knows her body well enough by the third to be smart about resting & hydration etc..
I would plan on short park days w/ a lot of breaks, early ADR's & if its ok w/ the MIL a dinner for just the two of you.
As long as you & MIL are planning on helping even more than normally, and you sound like the kind of DH who is, I think you will be fine.
Your DW will need a ridiculous amount of h20 a day, I believe Staples delivers cases to WDW resorts. You can also look up GardenGrocers (I think that is it ) web site they deliver to your resort also.
Your DW might be thinking that it will be easier to go pregnant than w/ 3 children, I hope whatever you do, you have a great time!!
You guys deserve some good wishes..hope you recieve some magic
Thanks for the kind words, but for the record I did not do it all by myself....