I look at how seriously a crossover should be taken for the Wold Newton Universe as a series of Tiers. So a crossover on tier 1 should be taken completely while one on the last tier should be brought up in conversation only to amuse you friends with the creator of that project's stupidity.
Tier 1: The works of Philip Jose Farmer. As he created this group and style of fiction his crossovers get the most attention attached to them.
Tier 1B: The works of the writers cited as in the Wold Newton Universe by Philip Jose Farmer. So this includes Edgar Rice Burroughs, Sir Arthur Conan Doyle, Ian Fleming, and so on.
Tier 2: Fiction and essays by Wold Newton researchers. (Essays can be on the Internet, but fiction can only be professionally published.) As they are writing for this universe itself they get highly placed on the tiers.
Tier 3: Pastiches that do not violate Wold Newton continuity. Such as many of the new Sherlock Holmes novels.
Tier 3B: Original fiction.
Tier 4: Movies.
Tier 5: Television shows.
Tier 6: Comic books. But only following Win Eckert's process of adding comic characters. You can see it Here.
Tier 7: Any Japanese crossovers.
Tier 8: Pastiches that violate Wold Newton continuity is some small way.
Tier 9: Parodies. Such as Doorlock Holmes, or many others.