Doctor Who is a show for children, an age that every adult alive has lived through, for better or worse. Sometimes, watching the show sends the same shiver of delight down your spine that picking up a good book did when you were nine years old-- but the reading recommendations you get as an adult are usually for novels and nonfiction bestsellers, not fantasy serials. We speak of the Star Wars novelizations in ashamed, hushed voices, or joke about the camp quality of vampire stories written for adult audiences. There just aren't that many quality book series for adults the way there are for kids; we don't get to return to our favorite characters the way we used to, and the fictional world is less a stable home than a series of nice hotels (or conceptual art-themed motels, Mr. Eggers).
The greatest series is arguably now televised, because with Doctor Who, there's no compromise. You're accepting the desire to be entertained at face value, and getting more. The ability to return to that universe week after week is something special. I don't think the community fostered by Doctor Who is frivolous or superficial. I think it's an opportunity to connect in an age of cultural fragmentation. I don't think any artistic output is frivolous or superficial if we engage with it in the same spirit as we engage with history or the news. It's just as telling.