My $0.02. You're mileage may vary.
Hoppers: You are going to be there during one of the 2 most absolute crowded times of year. With that in mind, I'm not sure hoppers are going to be worth the money. You are going to need as much time as possible in the parks to see things with those crowds, and you'd just be wasting time park hopping. Plus, you can't guarantee that you are going to get into certain parks as the day goes on, so you're best bet is get to your park early in the day and stay as long as you can stand the crowds. But, you can always add the park hopping option at any point during your trip if you decide you need it.
Golf Carts: I know there are people who love their carts, but they are not a necessity. And while they are fun to ride around the fort, again, if your main point of the vacation is to see the parks, there isn't going to be a whole lot of time for riding them around the campground. The busses (or bikes if you bring your own) are sufficient for transportation to/from parks.
HDDR: The HDDR is a great show, but it is very pricey. And again, at 2 hours, it's going to take some time away from the parks.
So, if I was planning a budget trip, with the main goal to see the parks, I'd actually skip all 3.