One of the more thought provoking things that came out of the OpenStack leadership training at Zingerman's last year, was the idea of the Triple Bottom Line. It's something I continue to ponder regularly.
The Zingerman's family of businesses definitely exist to make money, there are no apologies for that. However, it's not their only bottom line that they measure against they've defined for themselves. Their full bottom line is "Great Food, Great Service, Great Finance." In practice this means you have to ensure that all are being met, and not sacrifice the food and service just to make a buck.
If you look at Open Source through this kind of lens, a lot of trade offs that successful projects make make a lot more sense. The TBL for OpenStack would probably be something like: Code, Community, Contributors. Yes, this is about building great code, to make a great cloud, but it's also really critical to grow the community, and mentor and grow individual contributors as well. Those contributors might stay in OpenStack, or they might go on to use their skills to help other Open Source projects be better in the future. All of these are measures of success.
This was one of the reasons we recently switch the development tooling in OpenStack (DevStack) to using systemd more natively. Not only did it solve a bunch of long standing technical issues, that had really ugly work arounds, but it also meant enhancing our contributors. Systemd and the journal are default in every new Linux environment now, so skills that our contributors gained working with DevStack would now directly transfer to any Linux environment. It would make them better Linux users in any context, not just OpenStack. It also makes the environment easier for people coming from the outside to understand, because it looks more like what they are used to.
While I don't have enough data to back it up, it feels like this central question is really important to success in Open Source: "In order to be successful in this project you must learn X, which will be useful in these other contexts outside of the project." X has to be small enough to be learnable, but also has to be useful in other contexts, so time invested has larger payoffs. That's what growing a contributor looks like, they don't just become better at your project, they become a better developer for everything they touch in the future.