I think you're actually giving the spoilers too much credit. From my experience, so-called spoiled brats don't really get more benefits, they just get all the wrong benefits.
A particularly extreme example is my younger sister. She and her brother are biologically my half-cousins, but my parents took them in when she was three years old and later adopted them, because their actual parents are unfit (neglect, drugs, etc). At that young age, she was neglected, and I heard my parents suspect she was sexually abused. My own parents aren't exactly good parents either, but the way they neglect her is legal. They sent her to school but otherwise gave her no education and were poor role models, so she's not learning things like ethics, responsibility, problem solving skills, finances, other life skills, etc, but they did punish her when she failed at those things. They spent as little time on her as possible, often confining her and her brother to their shared room for several hours each day just to avoid having to deal with them. My step-dad emotionally, physically, and sexually abused her. When I physically abused her, my step-dad just sort of gave me a gentle talk to try to convince me to stop, which seemed dumb and hypocritical at the time. My mom hates her for some reason and doesn't seem to try to hide it. Nothing she can do is ever good enough for my mom. Even when she is well-behaved, my mom will find some flaw or just reimagine the whole situation. Not surprisingly, my sister is somewhat snotty, inconsiderate, and irresponsible but other than neglecting her chores, I can't think of too many things she's done recently that are hurtful of others. When she makes requests or demands of my mom, my mom will sometimes give in, but only after a lot of griping and criticism.
When she threatened to kill herself during an argument with my mom, my mom pretended to take her seriously out of spite, and the psychologist she met as a result said she was a spoiled brat.
My sister wanted a smart phone and my mom understandably didn't want to pay the increased price for the phone plan. Then her bio-mom got her a smart phone and paid for it, my mom was ticked and told me, "She has to learn she can't always get what she wants." She has to learn she can't always get what she wants!!? I kid you not, my mom said that to me about the girl I described above! Holy crap. She has been through so many horrible things. I wouldn't trade my life for hers no matter how freakin' awesome her phone is.
So, that's an extreme example, but whenever I see any details about allegedly spoiled brats, it seems to be along the same lines but without the illegal parts. Those people are brats because their life sucks and they're clinging to whatever good stuff they can get, but their sucky childhood has caused them to have crappy priorities. Actually having a good life won't cause someone to become mean and bratty (might even help prevent it, a little bit).