Spooks is a fun little game, but I was curious why the designer decided on five suits for the cards.
It occurred to me that Spooks, like some other fairly simple card games such as Lost Cities (which uses 5 "suits") and Battle Line (Which has 6 colors) are pretty easy to play in principle using a standard deck of cards.
By adding a suit or two the designer creates a product that's a little harder to copy (not impossible, as various threads on BGG attest) even if it doesn't change game play in any fundamental way.
Certainly the theme is usually pretty thin in these sorts of games. There's nothing especially "spooky" about spooks and it could have used just about any theme just as well -- or even no theme at all. To a large extent the theme just provides the artist with something to work with. As it turns out, I like the artwork in Spooks, but it's not vital to play.