Nice question!

I try to stick to my values and principles as much as I can. I deeply value most of my work, most of the time, and feel very lucky that I'm doing what seems to be the thing I'm best at. Like Max, we studied together at art school, my background is scientific (chemistry) and felt liberated during my new studies. I was very dogmatic at that time and didn't want anything to do with stuff I didn't value as much as other stuff (like commercials).

Nevertheless, working in sound(-art) doesn't always mean that you can choose. I found that out later in my career :) I'd love to work a bit more in documentary, than in fiction, but I take on what is available and pays the bills. The media type doesn't matter to me all that much (whether movie, documentary,theatre, online, museum or sound-art).

I am open to new ideas and philosophies in daily life and that flows through my work also. Most important to me is the kind of people running the show. I really have to 'like' the director and feel challenged by his/her story, otherwise it won't work very well for me. Advertisement, like I described above was a great example of what was not my cup of tea.

Making personal sound-art is something I try to do as much as possible and is closest to the idea of living/working by my values. But this is mostly unpaid or severely underpaid work that I do for my own satisfaction. Kind of like a hobby, which was the trigger that got me into the world of sound.

UPDATE: after your edit the question is a bit clearer. What makes my work more valuable: knowing that my contribution will help tell a story i 'support' will find a bigger audience. And hopefully in the same process show the audience that sound is a storyteller just as much as the visual part of the medium in play. Things I turn down: stories not worth telling (in my humble opinion) or in need of a better storyteller than the person in charge. or better said, projects by people on a different level of skill/experience/philosophy, and this could also mean that I'm not fit for the job. All in good times :)

As for me: I switched from an engineering study to film sound design, and I'm still happy that I did. Not that engineering would not have been interesting, but my heart was beating for this job.. I'm very happy not to work for advertisement-sound though. It earns you a lot of money but there seems to be quite a different way of working with people in that field. At least that is my impression so far... any opions on that?

In the past.. working on commercials for alcohol/gambling/fastfood industry etc.. was slightly soul destroying.

I've recently switched jobs and am I'm trying to make up for those times. Much happier!

Like many of us, we all got into sound for the love of it and this passion for painting a visual landscape with sound is a state of mind rather just a "job". For myself, at least, for the most part, this is true. And I say for the most part with the up most honesty because as my career developed and my comprehension of post audio increased, I still have had to do jobs that are soul destroying thus making me question the integrity of aspects the industry as a whole. Luckily I have had few of these projects- mainly television and voice over work for commercials. Not all of us can have the luxury of working on feature films for 30 odd years and we have to take on projects that are financed by companies which questionable business ethics. I ask myself, do you take on these jobs and if so why am I doing the job- for money only? And then I hark back to the first sentence of this answer regarding the love of the art form. By taking on these jobs, have I lost the passion and financial reward has taken over?

Luckily, I have had few of these gigs and the majority of what I do is morally harmonious. Documentaries, feature films, series. I refuse to give in to selling myself to the all mighty dollar at the risk of sacrificing my love for sound.

For me it's becoming increasingly difficult to write music and design sound effects for yet another Angry Birds or Temple Run clone.

But I'd rather pay my bills than stick to values at the moment. I don't doubt however that at some point in the future I will be able to pick and choose projects that I worked on, and it will be a huge relief.