I must confess we have never stayed at the Poly, but we've stayed at WL three times, once in each room type (standard, woods view, courtyard). The main reason we have not been to the Poly is price. I have not been able to justify the cost. I also like the fact that the lodge is all under one roof, whereas you have to walk between buildings at the Poly (a pain if it's raining an you want to visit a restuarant, food court or catch the monorail). If going at Christmas, I feel staying at WL is a must for theming and decor.
Our first trip was when my youngest was 2, and not being on the monorail was never an issue. We went back to the room for afternoon breaks on each of those three trips.
The bus from WL to MK takes less than 10 minutes, and having the boats were a great option. My kids loved riding them just as much as the monorail. The boats gave us access to MK, the WL campgrounds and the Contemporary. This opened up eating options beyond our resort to the campgrounds and all of the monorail resorts - what a plus! When we had early morning ADRs for Chef Mickey's, we were able to use a boat to go straight there versus taking a bus to MK and then walking or taking the monorail to the Contemporary. We had a bus or a boat to choose from for early morning ADRs to CRT at MK. And, if we did ever want to ride the monorail to MK or Epcot, we could do so via the Contemporary or first going to MK.
Just a personal word of advice, but if you can afford it and don't need to bring your own stroller, we thought it was worth it to rent the Disney ones. Not having to lug one on/off busses, the monorail or boats was a great thing for us. I know the price has increased recently, but I believe they still offer a discount if you rent multiple days up front.