You will not be far from Apopka Vineland Road and on that street are quite a few restaurants that are good, though not too fancy. If budget is not a concern, i would recommend Johnnie's Hideaway in the Crossroads off Apopka Vineland. [ not too far from where you will be staying and across the street to the entrance to Downtown Disney. ] I hope you'll have a car. It is a steak and seafood restaurant with excellent food. If you eat outside, they have tables with fire pits in the middle overlooking a lake. It is very romantic and pretty but quite pricey. It'll probably cost you around 100 $ for the 2 of you but that would include appetizers and dessert and maybe a glass of wine each.
If that is too much money, then go to the Crab House . it is in a small shopping center behind the Olive Garden on the corner of Apopka Vineland and Palm Parkway, not far from your hotel. It is mainly seafood but they have other choices and it's not nearly as expensive as Johnnies' but it won't be as memorable either but still very good.
Of course, you can always celebrate at any Disney hotel restaurant as i'm sure you will be going there at some point. Call Disney now to book it if that is what you decide as it's hard to get a last minute reservation there especially during the holiday season. A 30th birthday party at Disney sure would be memorable.