The parasites would have needed a lot of writing skill to become interesting again. They were a fairly ho-hum threat: the twin means of detecting them (loss of memory and a protruding breathing tube) were given in the introductory episode already, and apparently there were no lasting effects from possession. The only thing that was left vague was their ultimate aim, but it appeared to be a rather straightforward invasion plot here; there'd be little potential for upping the ante later on.
The Borg became interesting fairly gradually; "Q Who?" and "Best of Both Worlds" still left a lot to be explored and invented and reinterpreted. But the parasites would only have had one shot for reigniting the storytelling spark. If their possible return in "Q Who?" had not been an intriguing reboot where mystery was restored to their nature, I fear they'd have become a villain even less convincing than the Ferengi.
Timo Saloniemi
