I have the X-E2 and the upgrade to firmware 4.0 was simple and problem free. I looked at an X-E2S in the shop, and apart from the removal of the labels on the buttons (the upgrade 4.0 allows you to reconfigure the buttons, so the labels are not needed) and a slightly different handgrip, I couldn't see any difference.
So in your position I try to find the best deal on a new X-E2, and if it's a good discount compared to the X-E2S, go for it.
But keep the X-E1, as I've heard the skin tones are better than the E2 at higher ISO.
I have the X-E2 and the upgrade to firmware 4.0 was simple and problem free. I looked at an X-E2S in the shop, and apart from the removal of the labels on the buttons (the upgrade 4.0 allows you to reconfigure the buttons, so the labels are not needed) and a slightly different handgrip, I couldn't see any difference. So in your position I try to find the best deal on a new X-E2, and if it's a good discount compared to the X-E2S, go for it. But keep the X-E1, as I've heard the skin tones are better than the E2 at higher ISO.