For everyone who has been having difficulty understanding the Park Hopper Plus option, I know several people on here have explained it, but I thought I'd offer my experience in case it helps.
We have done this before with just the water park I add on and will be doing it this time with PH+. We're staying 12 nights/13 days. I don't plan anything for arrival and departure day because I don't know my plane schedule and there are too many what ifs. Those days, if time allows, can be spent at the resort pool, DS, etc. So I have 11 full days. I have 5 day PH+ tickets, so I have 5 days of Park Hoppers for the theme parks plus 5 visits (per person) to the water parks and mini golf. Last time we used one of these visits for Disney Quest, but that will be closing in July. I will also be purchasing tickets for
MNSSHP. So what I have planned is 1 day theme park followed by 1 day water park. The days before and after MNSSHP are water park days and on MNSSHP day we will spend the morning/ early afternoon in the pool at the resort, then go to the party. All 11 days are accounted for with 5 days in the theme parks, 1 day MNSSHP/ pool, and 5 days at the water parks. We will probably also hit up DS and FW on an evening or two after we leave the water parks.
Obviously, everyone has different priorities when it comes to their vacation. For us, the water parks are just as fun as the theme parks. They also provide a refreshing respite after a long hot day in the theme parks and a chance to sleep in a little if we need to so we aren't going from park open to close every day of our vacation. We could use the water park passes on theme park days, but I don't want to waste part of a day that I have reserved for a theme park in a water park. I maximize the value of those theme park days which leaves me wanting a "down" day afterwords that is still fun (waterparks).
Again, people think I'm crazy for only having 5 days worth of tickets to the theme parks, but I literally double the amount of days I can have fun by utilizing the water park add on (now park hopper plus) and it only costs $16 more per ticket to add the water parks to a 5 day hopper ticket (or in other terms, to add the "plus" to park hopper).
One last thing, it seems many travel agents do not fully understand how park hopper plus works. I had two different agents from different agencies (NOT Dreams! I'm sure they know what they're talking about) give me completely incorrect info about how the water park allotments could be used. Once I informed them they were incorrect, they called Disney and then told me that their entire agency (both of them) was unaware that water park passes could be used on separate days. So point being, if you are told you have to visit the water parks on your theme park days, this is NOT true. You CAN make a 10 day vacation with 5 day PH+ tickets if you want to with 5 days in the theme parks and 5 days in the water parks/ mini golf (but you don't have to). You can use your water park tickets any time within 14 days of your first ticket usage.