I think it's a bit too late to rename project, _now_. Even if they are not as spread as Wikipedia, Wikinews/books/source/ etc are at least recognizable: they have a growing identity. Instead of resolving the problem of their less "importance amongst common people" compared to the Wikipedia's one, you just confirm the difference: by saying "Wikibooks is now Wikipedia Books" you say: "Yes, you were right; Wikibooks was less important then Wikipedia, that's why we renamed it".
Another problem is: if you abuse of the brand "Wikipedia", you just make it weaker. As for now, Wikipedia is a strong brand: it makes people thinking at a _encyclopedia_. It's the encyclopedia bit that gives the identity. But if you use the wikipedia brand for other uses, people will get confused. People will start to not understand which is the real identity of the wikipedia: encyclopedia? Books? etc etc etc
Summarizing: this brand-rethinking is not a solution. Instead, it gives more problem to solve.
This solution will backfire.
Gatto Nero