Here are my 2 cents.
I am Mexican, and I am very against this rite of passage.
I think the OP was very right to say that it all comes down to money and how elaborate these things can get. I have 3 daughters I will not be having one for them ever!!
I don’t agree with our parishes allowing them so freely.
I have been to a few and I don’t like to attend them if I don’t have to have to. Why?
Well I think that most of the people that go are not concerned with the meaning of why they are having it in the first place. As PuzzleAnnie has said it is a introduction to society, also that this young lady will be chaste and stay a virgin till marriage. She is having a mass and making these promises before the church and her attendees.
Well let me tell you, at the party here is how it plays out; you go to the mass,
the photographer takes pictures of the court and the quincenera
the quincenera then is introduced with her entrance
then everybody eats and mingles
the quincenera and her court do a waltz
THEN!!!
the quincenera, and the other young girls in her court do a “Suprise” dance
which includes, dancing provacativly in front of all the guest, wearing tiny bitty clothes. and gyrating through out the dance floor, doing a routine dance like N’sync and this is supposed to be like she is grown up

And the parents are OK with this!!
Not all quinceneras do this surprise dance but it has become the norm. I was in a few when I was a teenager, when I turned 15 and when it was time for mine I said to my parents NO THANK YOU!!
It is a huge waste of time, money and energy. And I think it’s a joke, also a huge disrespect too.
I also do not know of any girl that has had one that did not end up preggers

after she was married.They all usually ended up pregnant, and very young with out a father being around. So where is this promise that they did before everyone and especially God?
It is not a sacrament. I cannot believe the Bishops would allow this, maybe they have not been to the actual party only the mass. I am sure that not all of them pan out like the ones I described, but my sister who goes to these things regularly tells me how they are.

and I cannot believe my ears.