If you had simply kept your mouth shut it would have been well enough. Why be so coarse?

索性 means outright, just plainly — if you had simply not spoken. 便也罷了 is the concessive shrug: that would have been that, no harm done. It is a real and slightly withering construction, the sound of someone telling you that saying nothing was an available option.

One sentence out of you, and it is enough to knock Mount Tai over."

The best line Tripitaka gets in the chapter. 泰山 is Mount Tai in Shandong, the eastern peak of the Five Sacred Mountains and the standing Chinese image for something absolutely immovable — the mountain emperors climbed to announce themselves to heaven. 倒 is dǎo here, to topple, and the exaggeration is enormous and affectionate: one word from Bajie could bring down the most solid object in the world.

Pilgrim laughed and said, "Better that I did not salute at all — and it saves a bit of effort into the bargain."

Pilgrim's contribution is to point out that he said nothing and is therefore blameless, which is true and entirely unhelpful. 省些力氣, saves some strength, is the kind of remark that is funny because it is so obviously an afterthought dressed up as the real reason.