I remember in my HS band we were very clique-y, but not in a bad way. Your section sort of became your family and then the people in your same year were good friends too. All of the section leaders were really good friends (and in my case, we still are good friends!) for example. Every section was like a club of sorts in the sense that we had special traditions. The flute section for example would have a party on the Friday night before our first competition. We would take an old pair of jeans, fabric paint, and any wide variety of things like bells, mirrors, etc.... to make 'spirit' jeans. We would wear them to our competitions. I personally never made spirit jeans being a buy, but I had shirts and hats and things.
Our section also had a few traditions for competitions. Our band would pray just before we went on field and instead of holding hands, our section would hold pinkies. We would immediately round up afterwards and do a section huddle and shout this line from Metallica's song: "Give me fuel give me fire give me that which I desire!"
It was great fun. Unfortunately I saw the end of these traditions. Most of these traditions were part of the fact that as a band we literally felt like an extended family. Our director was not only a phenomenal musician, she was a master at squeezing pennies out of nowhere (we were REALLY REALLY POOR as a band, so poor that we risked being shut down every year without the 'Save the Music' foundation). She also just had this way of being really personal and making you feel loved. She was awesome in every way. My Junior year in high school she rounded us all up in February and told us that she was retiring early because her family needed her. (Her granddaughter has severe mental and physical issues, and her daughter needed help). We all cried, but we knew it was for the best. Her replacement was honestly a lemon. I've gotten to know him after I graduated and I like him as a person, but as a director he was a total dud. The traditions stopped within two years of his appointment, the group cohesion suffered and within two years the band went from 75 members to 25 members.
So a lot of this problem that you are facing is from this type of problem I think. I see it in my school right now. The students are negative because the faculty are negative, and the faculty are negative because the students are negative. It's a vicious cycle. If you can undo this by trying to do the reverse of what happened to my band, then it may help. You probably will graduate before you see big changes, but it's certainly possible. I myself have turned groups around too, and it's tough.
I am the President of my music fraternity at my school (Delta Omicron). When I joined there were four people in my membership class. There were three people already in it, and they were leaving at the end of the semester (graduating/transferring). Total membership turnover in a semester. We had absolutely no connections to our past members to know our chapter history, chapter traditions, or frankly... anything about what our fraternity was supposed to be. Our membership class didn't really know each other that well, but we got along really well, and the fraternity was important to us. I was elected chapter President and membership, group cohesion, and relationships with other fraternities were my main goals for improvement. I did everything that I've mentioned here (and above). I've started traditions (families of big bro/sister and little bro/sister, family colors, group outings, group service activities (like serving dinner at the Ronald McDonald House, started activities that increase our bonds of friendship, and rebuilt the fraternity from the ground up. I've worked with the other music fraternities (who honestly tried to squish us out of existence... **didn't want competition, prejudice etc.**). I graduate in May and in the past two years that I have been President we have more than tripled in membership, become the second largest music fraternity in the university, gotten our name out in the community, earned respect from the other fraternities and have become very close friends. It makes me sad to know that I'm leaving them now, but it also makes me happy to know that I was the catalyst for pulling this group out of the grave.
It's all about personal dedication, motivation, self discipline, and just... putting in a genuine effort for the benefit of the group. You might not be around when things take root and cause the group to truly blossom (if it does at all). I worked very hard and I'm lucky to see my fraternity blossom the way it has. In terms of 'family' relationships I am so happy that I am going to be able to initiate my Great-Grand Little this April. Most members don't get to see that many generations of their 'family.' Ironically everyone in my family are flute players (four generations) and it's been dubbed the 'flute dynasty.'
Anyway. Sorry for the long rambling post. I just have had a lot of time to think on this topic over the past several years. I thought I would share my experiences.
We have probably 25 (?) members. In my flute section alone we have 5 flutes and I believe there'll be at least at 7 next marching season. I want the numbers of members in our band to grow but I have no ideas. Students in our band tend generally tend to drop out for two reasons: 1. The band director or 2. Getting made fun of. We lost one of our best snare drummers because of reason 2 and lost a quad player from reason 1. 
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