We recently booked this for our grandparent's 50th anniversary celebration trip to the World.
They LOVED it.
I'm not sure if it's the same experience for everyone (though I'd imagine that they are for the most part) but they received lots of extra attention from the host and the servers. The menus they received were shortened versions of the regular menu and were personalized. I'm not sure how they determine what goes on the menu. I think it's likely their most popular dishes. My grandparents' menu included, for example, among other things, the Sonoma Goat Cheese ravioli, the Pork Tenderloin, the Oak-fired Filet and the Valrhona Chocolate Cake. My guess, though, is that if there wasn't anything on the personalized menu that piqued your interest, they would cater to what you had a hankering for.
I believe it included wine or champagne and they had a beautiful view from their seat by the window. I'm not sure if this is "included" in the package or if they just lucked out.
As to whether or not you should keep the package, well I think that depends on what you're looking for. I'm not sure if with the package you'll get the full range of the Grill's menu. And it's an amazing menu. I would probably talk to Disney Dining to determine exactly what's included and then gauge it against what you might want to order/experience.
My BF and I ate their last week and we didn't have the Sweetheart package and it still was a perfectly romantic evening.
Congratulations to you and best of luck!