One more thought...
I write thrillers - literary thrillers, but thrillers nonetheless. If I were writing in a different genre, the minutaie may be more important to the storyline. If it were romance, the childhood tension between Alex's mother and father would be pertinent to how she deals with relationships. If it were mainstream, then the book may very well have been about Alex's past and how it's shaped her. I don't think it's as crucial to the development of a thriller, though. Ken Follett, for instance, didn't delve into why 'The Needle' was a bloodthirsty killer in "The Eye of the Needle". He delved into the hero's background just enough, but it moved the story forward; it didn't remove focus from it. And, Leon Uris did it to a certain degree in "QBVII", but again, it was necessary to the story.
Now, for Blink, I've gone deeper into the characters. Blink isn't a thriller. Actually, I'm not quite certain what genre it fits into, but while it does have some thriller elements, it's not strictly a thriller. It'll probably fall into SF, they way Fahrenheit 451 fell into SF. And AWJ is a mystery, so there's more characterisation in it.
IMO, how deep you delve into your characters depends on the genre. As always, write the story how it needs to be written.
Just thinking out loud.
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