It really depends on several things: how many times you've been to WDW; how long you'll be there; ages of the people in your party (the very young and the very old generally don't enjoy the water parks as much); and what kind of budget you have.
Since you've indicated the budget is an issue (which it is for the vast majority of us) and it's your first trip, I would skip the water parks fun & more upgrade unless your trip is pretty long, say, longer than a week. There is so much to see and do in the main parks and resorts alone that you won't even miss the water parks. We've logged 8 trips in the last 13 years, and just visited a water park for the first time on the last trip.
I do agree with you that the hopper option is a must have, especially for a first timer. You never know if you're going to love (or not love) one park more than another, and it's nice to have to option to leave and head somewhere else to make your trip more enjoyable. After you've been a couple of times, you'll have a better sense for what you like and what you don't like, and could plan a trip in such a way that you could do without the hopper option. But not for a first trip.
Congratulations on your first trip, have fun, and welcome to the DIS!