If the gentleman with the Rheinisches Wörterbuch could help again...
Spökerisch is from Heinrich Böll and thus quite possibly Rhenish again. It might mean potty or dim or eccentric from context.
(Er) war nicht gerade ein Spinner, aber doch ein bisschen spökerisch.
The word probably stems from "Plattdeutsch", a dialect (or even an own language) spoken in Northern Germany.
They know the word Spökenkieker — people who can tell the future (mostly bad events coming up) or see ghosts. "Spuk-Gucker" or "Geister-Seher" would be a direct translation. Sometimes people who tell scary stories also are called Spökenkieker.
Spöken are ghosts or spooks (see the similarity?), so somebody who is spökerisch might be a bit spooky or strange.
