We can almost certainly use 100x as much code as is currently written. There's a ton of throwaway code that, if written, would produce small but nonzero value. Certainly 100x as much code wouldn't produce 100x as much value though. I suspect value per unit of code is one of those power law things.
I think we have a tendency to overestimate efficiency... because of the central roles it plays at the margins that mattered to us at any given time. .
But the economy is bottlenecked in complex ways. Market demand, money, etc.
It's not obvious that 100X more code is something we can use.