The onsite guest perks seem to be only that they get the band at this point in time (see quote above from Disney when they announced MyMagic+)
I'm not entirely sure that this system is specifically designed to give advantage to the onsite guest anyway. In the parks every guest will spend money while not in lines, not just on-site guests, so it makes no sense to only go after on-site with this. They don't have to give anyone perks, just keep everything simple under one class of system. (The difference between ticket and band seems minimal from what I can see at this point.)
This just doesn't seem like a system designed in order to entice people to on-site resorts, but primarily to keep them out of lines and from wandering off-park (i.e. to universal.) I'm not saying this system wouldn't result in more attendance on-site (which I'm sure Disney would love), nor am I saying it was designed with off-site guests in mind. I'm saying they seem more focused about what happens
in park not which resort people are going to.
If they really wanted more people to stay on-site because of this system it would have been designed far more on a class system, even with different access amongst the more expensive disney resorts. As it stands, the basic components (touch to enter, pay, and redeem fastpass+) are available for everyone, off-site, basic, mod, deluxe.
See this article for a Disney statement on their aims (what they admit anyway)
http://www.businessweek.com/ap/2013-05-07/on-the-call-disney-cfo-explains-mymagic-plus.
So if we can get people to plan their vacation before they leave home, we know that we get more time with them. We get a bigger share of their wallet
Nowhere in that article does it mention anything about encouraging people to spend more time in Disney resorts, but about getting people to spend more time at Disney full stop, which includes the parks. I think It's more about ensuring people don't leave WDW parks to go to other parks.
I can see some small benefits being given like you posted but some people seem certain they will get more FP+ for staying on site. I'm not saying i'm definitely right, but I can't see them giving a fundamentally different level of service to on-site guests, like more FP+. It's not neccesary, as in-park everyone has money to spend, and Disney will want tour groups, on-site, off-site,
everyone to spend more money.