As a translator who billed approximately 750,000 words last year, yes. Speech to text software is another good tool for circumventing this bottleneck that many translators use.

More precisely, is the effort spent on improving typing speed beneficial for the cost put in?

Typing faster is always going to be a benefit.

I think it would be too much effort for most people to get to 150wpm, or to learn stenography.

But, on the other hand, if people are typing 30wpm, they would benefit from training to improve their typing speed.

At this point, my keyboard is the bottleneck. I regularly type 100-120wpm and can hit 150-180 peak.

if you're using a keyboard, slow typing speed is overhead on getting your job done.