I totally understand where you're coming from, as someone basically in the exact same boat, I think about this question a lot.
I don't have a ton to add to what @smceccarelli said, I think that's a really good, succinct way of thinking about it.
There's value as defined by others (which you might not feel yourself, but which nonetheless, others feel and are willing to shell out money for) and then there's the FEELING of doing something valuable, which has much more to do with a kind of inner purpose or personal mission. I think the important thing is to realize that these are two different goals which require different steps to achieve.
For me, with my design work, I might not feel a sense or purpose when I'm working on a project, but I can tease that apart from the fact that this person one the other side clearly thinks for whatever reason that what we're doing is of value, either to them or to someone else. If I can at least intellectually understand that, it helps, but I have to be careful not to mix this up with my personal sense of what's valuable, otherwise I just get confused.
Thanks for asking this question! It's always so great to talk about these things and hear how other people think about it.