To give you a tangible example, GrantTree's mission has been, from day one, to help UK startups, by being one of the better players in the UK startup ecosystem. It's a tangible positive difference which we can all feel we're making.
Of course, making money is also important, if only because money allows us to hire better people and do a better job, and it was also a primary reason of starting GrantTree... but it's not a good enough reason to put all the energy to grow it past the stage where it is an extremely profitable hobby, to the stage where it is a genuine business.
The qualification of "worthwhile" is really subjective to the point where unless you're literally doing something truly impactful (which I define as value + massive scale, e.g., cure to cancer, etc.), your value is at best a surface scratch and at worst a fad.
Consumer oriented startups like Snapchat spring to mind, which seems to have both a questionable mission statement + a shameless pursuit of founder enrichment. Not judging (I'm jelly), but I do think it serves the greater point I'm trying to make.