I liked the cocoon scene too, but as shot, I think I can see why they left it out of the original cut. The lighting was less than successful, and probably the sculpted design too, in that you can't really tell what you're looking at unless you have time to really examine the frame. Especially the Brett-egg. I don't think it was painted in metallic colours, it's just the glaring highlights from a gloss surface that makes it look that way. Probably Derek Vanlint, the DP, would have liked more time to light it better.
As far as the crab walk goes, it's great that Scott was experimenting with different ways to hide the man-in-a-rubber-suit effect, but just like the test of Bolaji Badejo creeping through the unfinished Nostromo set (that I know everyone's seen so I won't bother linking from YouTube), you can instantly tell there's a human actor inside the costume from all the little nuances of weight-shifting that Badejo does. We're all so familiar with how the human body moves it's pretty hard to fool the human observer.
Same with the out-take of the alien throwing Parker against the wall then stepping in to finish him off. It's subtle, but instantly recognisable from Bodaji's movements that he was completely blind when he had to step forward, as he kind of shuffled one foot forward to feel out with his toe where Yaphet was lying in case he tripped over him.
So, interesting out-takes, but they were wise to edit them out.
TC