Hi Diane and welcome to the Disney Parks Moms Panel.
I love that you are already planning your 2017 visit to the Walt Disney World Resort - you're a girl after my own heart!
Firstly, it is indeed possible to upgrade from the Quick-Service Dining Plan to the regular Dining Plan and it is absolutely worth it as far as I am concerned. There are so many fantastic Table-Service restaurants to choose from including
Character Dining,
Fine/Signature Dining and
Dinner Shows.
My family also like the fact that having a sit-down meal each day gives us a chance to cool down whilst taking a break from touring the parks. We also love the convenience of having paid upfront (aside from gratuities) for our meals which reduces the amount of spending money which we need to budget for.
There are a handful of Disney Resort hotels where it is possible to walk from there to Disney Theme Parks. It is possible to walk to both Epcot (World Showcase entrance) and Disney's Hollywood Studios from Disney's Beach Club Resort, Disney's Yacht Club Resort and Disney's BoardWalk Inn.
It is also possible to walk to the Magic Kingdom Park from Disney's Contemporary Resort.
Wishing you a magical holiday filled with memories which will last a lifetime!
Emma