I hate the idea that Giles comes from money, and I rebuke it, I don’t think we should accept it. It's convenient for the comics in particular that Giles has an independent source of funding, but I think that convenience comes at the expense of character.
Because having money changes your world outlook. Having generational wealth and never really having to worry, and knowing you have options open to you changes your outlook. I'm not saying everyone from the same class is exactly the same, but we *can* make generalizations. The conditions you exist in shape you. And in my experience, having known a few people who grew up wealthy, having that level of security and comfort shapes their outlook quite a bit. They start to take things for granted.
Giles clearly isn't working class, but I will argue that he's middle class. I think one of the dividing lines between middle class and generational wealth is that, however comfortable middle class existence might be, there's still the acknowledgment that you have to work for that comfort. You have to do well in school and get a good job not just for the sake of pride but because if you don't, you aren't going to keep up that lifestyle. You don’t have a trust fund to save you. In the comics, Giles has a no-job needed amount of money and I hate it.
So, what really characterizes Giles when we're first introduced to him is his enthusiasm, his sense of adventure. He's stepping into the world of monsters, and he's excited about it. And I just think that attitude corresponds to someone who, up to this point, has had to put up with a certain confinement, a certain routine, and certain obligations. Someone who has been *working* towards the life they want and now has it. It doesn't match up as well with someone who had the resources to travel or otherwise pay for some kind of hit of excitement.
Giles also has a definite work ethic. He approaches training Buffy in a systematic and diligent way. He also carries out his librarian job extremely competently and without complaint. His competence speaks to someone who has had a job throughout his life.
Compare that to Wesley, who I think you could argue comes from a bit of money. He has the air of dilettante in everything he does, and is motivated by neuroses. Or Cordelia, who has utter disdain for mundane work.
Season 1 Giles didn't have a defined backstory. The whole "Ripper" thing is something they came up with in season 2. And then Giles coming from money was a way to (1) justify using Tony Head's house as a shooting location s7, (2) pay for things in the comics. But since Giles' monied history was such a late addition, it didn't inform his character at all. The writers defaulted to writing a middle class character because they themselves are PB/middle class. Without consciously choosing something different, they imbued the character with their own class. But then when they decide to define Giles' class much later, it feel disconnected, because it hadn't been part of him the whole time.
I don't have a neat conclusion. Just, let's ignore canon when it's sloppy and written for convenience rather than character. ( @mmhhch )