I ask .. why wouldn't a drummer learn ambidexterity if it meant that their playing would be unlimited and probably increase one's skill level? It doesn't mean you HAVE to play that way live. I watched Cobham from side stage once and the freedom that man enjoys because he can play open handed is astounding, same for Dom.
I would say from a learning stand point that any amount of time spent increasing your prowess on your less dominant side will automatically make you better in all areas of your playing .. time, feel, meter, independence, rudiments etc. By the very basics of it, you are exercising a part of your brain and body that doesn't get utilized fully ... a win win for sure.
When I did teach, I taught every new student to play open handed and they picked it up very quickly. In fact all my former students that I taught open hand playing to do not fully understand why crossing over is beneficial at all ... but they can play that way too if they want! They are limitless in their set up and ability! Always a good thing in music.