There was a thread on this same question somewhere around here (I was just reading it yesterday...! Now can't find it

). Anyway, you will get many opinions on this. You don't say when you're going, but I read another post saying that in the summer, these parks fill up so fast that they often close (as in before noon) when filled to capacity.
Also, with this being your first trip to WDW, you will have plenty to do seeing the parks. However, with 7-day passes, you also can go at a more relaxed pace. Do you want to take a break in the afternoons? Many are content to do so at their resort pool (us among them), others will head to the water parks. I wouldn't think you'd get as much of a true rest there, but it certainly will be fun! Depends on what you want in that respect.
We aren't paying for the Plus option this time around because we want to concentrate on the parks. My kids are 9, 6 and 4, and more anxious to do the theme parks than the water parks. If we feel like taking a day to do Typhoon Lagoon, we'll decide then and get tickets just for that day. Since I know we won't go more than once, it's not worth the cost to me to get the Plus options on my tickets. But that's me.
Good luck in your decision!