Resolved: What will my rating be?
Upgrading has no impact on your rating. Your rating is driven purely by wins and losses. Of course, your rating could improve after you upgrade if you use the many game improvement tools available to premium members on this site.
As Sorg67 said, your rating is a reflection of your chess performance. Upgrading to Gold/Platinum/Diamond membership won't automatically make you perform better. However if you watch the chess video lectures made by various chess masters, use the Chess Mentor and Tactics Trainer programs often, which upgrading allows for, you may see yourself performing better in chess matches.