Hi Sue,
I love
Disney's Old Key West Resort. The laid-back vibe there is so wonderful. I always come away from a vacation there feeling peaceful and relaxed.
Though I have never done it myself, I did some searching and have found that you can indeed walk from Disney's Old Key West Resort to Downtown Disney. This is a fairly long walk, so you should plan time accordingly. There are also no water fountains along the way, so bring yourself a bottle of water for the stroll. Finally, the path is not lit, so please only walk on it from dawn until dusk. There is a lovely photo tour of this path on the unofficial site mousesteps.com. You can visit that site and search for "Old Key West" - look for the article which is a Photo Tour of this walk. I think that it will give you a great idea of the walk.
It is very exciting that Downtown Disney is becoming Disney Springs! The
Disney Parks Blog ran an article about Disney Springs earlier this year, which lists 2016 as the completion date for Disney Springs, so it will not be completed by your trip in 2014. I am not sure if the Disney Springs project will impact the walking path from Disney's Old Key West, and if so when it might happen. I suggest monitoring the Disney Parks Blog for further information and updates on the Disney Springs project.
I hope that this information is helpful for you, Sue! Have a wonderful time planning your vacation, and please do not hesitate to ask if you have any further questions.