There is never ever a reason to grind monsters in Guild Wars 2.
Because in the end, people still want a mechanical experience, not a dynamic one. Guarantees are something gamers have come to expect.
Certainly seems that way, and it's actually pretty depressing. They've set up this whole dynamic world, and in the end a lot of players "don't want to miss anything" and need to make sure they're doing things "right" at all times. I'm kind of glad that the wiki is far from complete at this moment because it means people need to use the heads, at least for some things.
I probably shouldn't be ragging on people for the way they play, but it feels so... against the philosophy of the game to be meticulously plotting every upcoming interaction.