Hi Samantha,
Firstly, what an amazing upgrade you received upon arrival at Disney's Grand Floridian Resort & Spa last year - I am always daydreaming about staying in a Club-Level room!
I wish I knew what the secret formula was for increasing your chances of being offered an upgrade. In all of my stays at various Deluxe, Moderate and Value Resort hotels over the years, I have never once been upgraded.
I honestly do not know if by checking-in online you would be lowering your chances of being upgraded on arrival. According to the
Online Check-in - Frequently Asked Questions, room assignments are not provided when you use Online Check-In.
The main benefit of completing Online Check-In is that you begin your check-in process in advance of your arrival and therefore, should experience reduced registration time upon arrival at your Disney Resort hotel.
If this is not a primary concern and you do not have any specific room requests to make, I might pass on completing online check-in in the hopes that you will receive the same luck that you did last year.
Wishing you a magical holiday filled with memories which will last a lifetime!
Emma