That's the thing that the "2 massive leagues and play each other twice" brigade fail to address.
The drop off in quality, interest and resources when you go into the 2nd tier would be catastrophic.
I abhor the OF dominance of our game and its endurance, but the 4 league structure, now it has meaningful playoffs* is magnificent. I love it. The continuum of size of club is just about right (now FFC are back on the up, at least ), and there's enough jeopardy that big teams like Hearts, Hibs, Dundee Utd can semi-regularly go down.
*Next step is auto relegation for Team 42.