I'll add, disgal, that I do think FP+ does benefit the Resort-stayer subtly and indirectly over the off-siter.
If I can be so crude as to generalize (Aaah! The scourge of the internet!)
Resort-stayers tend to favor the immersion experience. They want to do more things that are not related to riding the rides. They are generally content to get on fewer rides. If they get on a few, quickly, and get on the ones they wanted, they consider the day a pretty good success.
Off-siters tend to be value seekers. Obviously they're choosing lower cost off-site hotels for a reason. They want to spend less to get the rides they want. They are not as into the immersion experience, evidenced by the choice to stay off site. So they're looking for more no-frills just get me on the rides type of vacation.
Both are fine vacation types... there are plenty of both types as evidenced by 30'ish WDW resorts and just as many off-brand resorts nearby.
FP+ gives both "groups" 3 rides per day.
Resort-stayers think this is okay. They're there onsite. They had an easier time getting to rope drop. They have a shorter trip home. They can leave midday easier. They're there to tour anyways, so even during busy times, going on the Haunted Mansion via standby is still pretty cool cuz they actually like to see the stuff in the line. They get on 3 rides quick which helps them accomplish their day, and they go on other stuff standby, really, pretty happily. Yeah they may wait for Soarin *or* Test Track... but, while waiting for Soarin, they watch their kids play w the screen thingys or while waiting for Test Track they customize cars. It's all good. Happy to get FP+
Off-siters think this is bad. It takes them longer to get to/from the hotel, they have less time there, and they can't readily make use of the midday busy time cuz they're stuck at a park, with a 2+ hour round trip to go back to the hotel. They've been on the HM a million times and couldn't care less about the graveyard attractions or the animatronics in some other queue. They just want to get on the rides. Off-siters and AP holders have also gone a lot more so these cursory activities interest them much less. "yeah we saw the graveyard 20 trips ago". So them getting only 3 FP+ is kind of annoying cuz they'd rather get more and ride all day.
Now between the two, each group got 3 FP+, but it sure seems to benefit the Resort-Stayer / Casual Tourer so much more. Resort stayers are paying Disney $250-$700/nt. Off-siters are paying Disney $100/nt. So obviously Disney is pushing out this new system well knowing that altho it gives each 3 FP+, it's going to attract more Resort-Stayers because it suits that style of touring more.
Thus, I think FP+ indirectly benefits Resort-Stayers moreso than off-siters even tho they get the same number of passes.
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(Pls don't anyone take offense for the generalization. It's just an approximation... like saying "men are on average taller than women" does not mean "all men are taller than all women". Keep this in mind. I don't mean to suggest there is no crossover between the two groups)