I vote #2. #3 gives them too much credit, and #1 not enough.
Although it may not be so much that real monsters catch more eyeballs as that messing with the formula (in a reboot) catches more eyeballs. By now, I've seen enough direct-to-video modern Scoobies that I expect them to be supernatural (as well as inferior in other ways), so maybe next time they'll go back to fake monsters?
Scooby-Doo and the Witch's Ghost is probably the worst. It's not just that the witch is real, which as I said I expect now, but its (positive!) references to Wicca are so uninformed and trashy that it's actually an insult to Wiccans too.
Edit: Possibly Scooby-Doo! Mystery Incorporated is exactly this return to fake monsters. I don't know, I haven't seen it. Since it has an ongoing story arc, they may decide to make a monster real in the end.
A great column by Chris Sims at the Comics Alliance.
Excerpt:
Tim Minchin fans may recall him mentioning Scooby Doo in a similar light in his beat poem Storm, and it's been brought up on Less Wrong before.
When viewed in this light, Scooby Doo really is like an elementary version of Methods of Rationality.