I think that the answer to this is (of course) multi-part.
First, I think Staff needs to lay out their own expectations for the game clearly and concisely. I don't remember who suggested it, but I love the idea of a game mission statement: This is the game we want to run, and here's why. One to five sentences, two very short paragraphs tops.
Here was the mission statement from T8S:
The Eighth Sea is a game of piracy and the supernatural, of wooden ships, iron men, and the dark myths that slipped through the cracks of civilization. It will explore the edges of reason and the tensions between civilization, outlaws, and the unknown.
While there will be no prohibition on individual CvC conflict (piracy and the supernatural are dangerous), the focus will be on collaborative CvE, on determining the cause of The Storm and on working together to return to the world of the real. We are playing a Hollywood version of history, with similarly Hollywood interpretations of real-world religions and myths. There will be darkness, but there will also be swashbuckling and derring-do.
Second, I think Staff need to walk the walk. This is where we screwed up. We didn't have enough piracy in our pirate game. Too much supernatural, not enough piracy. But whatever vision Staff articulates, they need to follow through on it in every single encounter with players.
This is because Staff (and the behavior they allow/encourage) sets the culture of the game. So if you want your game to encourage group play, you need to celebrate those people who share the spotlight well. If you want to discourage spotlight hogs, you need to close off avenues of solo progression and direct them to ways in which to work with other PCs instead. And then those ways have to work if they actually follow them.
The more that player actions (and by this I don't mean just that they solved the plot, but how they did it) are shown to clearly impact the state of the game (not just showing up on a bbpost, but actually changing how things happen going forward), the more I think that players will be inspired to actually take action.
Thirdly, yes, I think that those players who try to spotlight hog need to be talked to, quietly and individually. On the flip side, I think that those players who are great in scenes, but don't really engage in the story need to be talked to also, to find out what's missing for them, and to encourage them to get involved (of course, going back to point two, once you find out what's missing for them, I think you either need to change it or let them know why you aren't changing it).
I don't think that this is a code issue in most cases (although maybe Teamwork Rolls could be emphasized in the difficulty of actions, to discourage lone-wolfing even in requests?). I think it's a cultural issue, not a code one.