I did some research and stance and open hand last year. I posted it on the officials:
http://forums.play.net/forums/GemSto...et_newest=true
(also http://forums.play.net/forums/GemSto...et_newest=true for 702 vs 711)
(also http://forums.play.net/forums/GemSto...et_newest=true, difference between 1x/.5x and 1x/1x)
tl;dr: I saw a small increase in appraised skin quality from kneeling/stancing, but not real impact on skin value. It was all statistically insignificant. I never got enough trials on any of those posts to lock down small effects.