You seem to be suffering from "too smart for your immediate company" syndrome. I know the feeling, in regard to both the friends and family situations. It's frustrating to think that being intelligent and insightful is often the exact set of criteria for people who are often ignored. Addressing the issue with your friends- I have always been in the same situation (and still am)- I'm the "plan B" when it comes to entertaining company, and nobody ever responds to what I have to say unless it's something stupid. The fact is, people like you and I are prime targets for one-sided conversations. I'm a good listener, and while no one verbally acknowledges that, it's become clear to me that a lot of my less intelligent friends find solace in being around me when they have something to talk about. I don't know a damn thing about cars, and neither do any of a particular friend of mines aquaintences- but I'm the one who will listen to him ramble on about his day of work at the car dealership. He doesn't realize how desperate he is to have someone to vent to, and he usually won't even entertain any conversation I try to start about something else. But that's the nature of people who aren't intelligent, mature, or patient enough to be outwardly grateful for having someone like you or me to take their minds off of things. They're not trying to be ignorant, they just get hung up on their own concerns- their brains don't have any room left to consider what you have to say with any importance.
But what they are aware of is that you're smarter than the average bear, and you'll listen when they need to talk. When I speak up in a gathering of my friends, the problem isn't that nobody can hear me- or even that nobody cares- it's that none of them have anything intelligent to say in response. And I'd be willing to bet that's a large part of the case with your friends. My friends don't see it as insensitive to ignore my problems, usually because they know or assume that I'm smart enough to figure it out for myself. It's like trying to bring up a discussion about religion at a superbowl party. It just makes everyone uncomfortable to suddenly realize that- whether they wanted to discuss it or not- they don't have anything valuable to add to your thoughts on the matter. The only thing a bunch of football-heads can think to do in that situation is just ignore you and hope you don't bring it up again. And that's just one specific example. The point is- your friends probably do value you and appreciate that you can listen and offer feedback on their thoughts and musings. Otherwise, they wouldn't hang out with you at all (unless they're using you for money, weed, or food, but it doesn't sound like it's that kind of case).
As for your family, I'd be willing to bet the problem has similar roots. Especially when it comes to parents- because after a certain age, most folks tend to be low on energy, and are only willing to expend it on harm-reduction. When you do something wrong, it's an alert, and their "I need to fix this quickly and aggressively" sense is triggered. When you're in the right, that's the time they use to relax, especially now that you're a young adult. They may not realize that it comes across as insensitive and careless, but they want you to start acting independently, and deliberately, and not just for their praise, but for your own self-satisfaction. I don't know what the situation with your brother is, but don't simply assume that everyone just thinks he's more interesting. Maybe they're just more worried about him- maybe they get the impression that you're more self sufficient, but he might need a little more attention to keep him on track. Like when someone owns a cat, and a dog. They may not necessarily like the dog more, or think he's more interesting, but they know that if they don't take the cat for a walk, it's not going to get angsty and wreck the house. If they don't buy a leash for the cat, the cat isn't going to run away and get lost, but the dog sure as hell will. So in the end, the dog receives the majority of the attention and monetary investment, but it's only because the cat doesn't *need* it, and people only have so much money to spend, and only so much love to show.
People are only capable of engaging other people of similar intelligence, and people like you and I are a step above the average in that regard. I can tell from the way you write, that you are a deep thinker, and a generous friend. When you give what you can, and it's more than everyone else is able to return, it can seem like nobody appreciates your kindness, and your patience. But consider how you would feel, being friends with someone who was always happy to listen, and who never made a fuss when you didn't have anything to say. It would be easy to think only of yourself around that person, and hard to feel sorry for them if you knew just how smart and mature they were. To blow them off in favor of finding a companion who was more your speed would seem a reasonable thing to do, and I'm certain you wouldn't hesitate to correct them when they were wrong. Again, I don't know the entirety of the situation, and maybe your friends are just jerks- but it still makes things easier to swallow when you give people the benefit of the doubt. And don't think you're looking down your nose at the world when you really are surrounded by ignorance.