2 Investigators in Mansions of Madness
Multiple Investigators

After my last 2-Investigator game, I was explaining this issue to one of the players and proposed the "scale the time between events solution."

She said, "Why don't we just each run two adventurers?"

Why didn't I think of that?

I think that from now on, MoM will be a 4-investigator game, with players running enough investigators to make up the difference. It works great in dungeon-lords.

EDIT: There are additional benefits to this solution:


Scaling the time would drastically reduce the sense of urgency in MoM. 
Not only the number of actions but the reduced breadth of abilities is unaccounted for in a fewer-than-four-Investigators game.


This is decidedly my preferred way to play the game now. I would only consider less than four Investigators as a way to bump the difficulty for players that consistently win too easily.