In ETK Pavel quotes a Russian hand-to-hand expert as believing that, for a fighter, 50 snatches lefft, 50 right, with a 24kg kettlebell is a point of diminishing returns, i.e., time to focus some of your time/energy on other things. In a recent thread, Pavel put a double BW deadlift in the same category for most types of athletes.
You really have to look at this in two ways....
* What incremental benefit "to fighting" (or whatever your frame of reference is) would increasing your snatches have... we will call this "B"
* How much does it "cost" you to get the incremental improvement (in terms of time, equipment, coaching, etc. converted to a common denomination)... we will call this "C"
In training and in life, we want to increase our incremental return, or B-C. This is over all training activities.
In this case, I believe that in increase from 20L/20R to 50L/50R, you are increase the qualities that make you a better fighter (grip strength, strength endurance, focus, tension during rest, etc.). Also, you can make this increase relatively quickly (ask some people who took some of my advice

)
Let's say that you want to go to 70L/70R. To do this, you will have to:
* Learn GS specific techniques, which contribute little to fighting
* More focus practice in GS, which will mean less focus on fighting practice for those whose time is limited
* It will not have the same relative benefit as going from 20-50
In Dan John's example, it is similar.
* Improving his bench up to a point made him stronger AND more powerful
* After that point, he was increasing limit strength (max F) at the expense of power/throwing (max F*v)
I had my own example of this. I used to a be a pretty high level soccer player, but I weight training was focused more on bodybuilding routines than strength training (I though they were one and the same, boy was I wrong).
At first, I got bigger (163 to 170) and stronger and faster. When I got up to 185, I was bigger, faster and slower, even though body comp was the same. When I took a powerlifting seminar, I practiced box squats and speed benches, and I got faster because I trained for speed.
If you want to get better at whatever sport you do, you need to work backwards from your "desired outcome", and plan your exercise program to get that outcome.