One of the lessons of writing the Silverline project has been about what "the spotlight" means in a game.
Time on camera
The meaning of "spotlight" as I've seen it most often used in gaming is just "time a PC gets to spend on camera", or "time in which a PC's actions are being narrated and responded to". In this sense, the spotlight can and should be shared - if multiple PCs interact, or cooperate in a scene, they are all in the same spotlight.
The way I'm using the spotlight in this sense is to try and give each PC roughly the same amount of dramatic oomph - sometimes a short but impactful scene counts for as much as an extended pedestrian scene. And to keep everyone illuminated, I'm doing my best to see that the spotlight is often shared by 2-3 PCs at minimum.
Backstory and life
Another way to interpret the spotlight is "time in which the PC's life and history make an appearance". Even if the Guardian Ghost gets a lot of time to make decisions and take action, if his Legacy, his family, and other factors aren't making an appearance, did he really get as much spotlight? Probably not.
So in that sense, it's important to look for ways to incorporate PC life stories into the current action. But there's another thing the spotlight can do, if shone on these things.
Driver of drama
It can sometimes be a challenge to weave these elements into an ongoing story. The advice of "ask the player for suggestions" does nothing when I'm the only one playing, so I've gotten to reflect on it a little more. Some PCs' backstories or natures resist a shared spotlight - "why would I be bringing my team to my secret lair?", "why would I be revealing my deadly real origin?", and so on are all questions a player might raise. Sometimes the answer is "don't play a character who won't share". But other times, the answer is "strip away a PC's defenses and resources until they are forced to go for help".
In the Menagerie game, my PC Leo did this - moved in with another teammate after his own home was compromised. I did this partially because it was the logical outcome of the fiction, and partially because it brought my PC closer to another one, making room for more shared scenes and action. In Silverline, forces will necessarily appear that push the PCs into trusting each other with their darkest secrets. In this sense, having a spotlight forces me to ratchet up the drama, to include elements that ought to be included.