Hi!
Unfortunately, here's the deal: Think of the plus features as individual tickets. So if you've got a seven plus four, then you've got four individual plus tickets. They are each good for one day at one attraction, with unlimited re-entry rights to that park only. In other words, yes: if you go to BB today and PI tonight, that's two plusses. You can go to BB today and spend the whole day running in and out and only burn one plus. But step on PI, and you've burned another one. If you want to do more plus-parks than you have options for, it's always better to use them for the waterparks. PI's cheaper, and they have a pretty good deal for a six day pass.
Pat