Wyches w/ wych weapons are extremely effective in assault, but considering how much they cost and how fast they die to even lasgun fire, I'm not sure how warranted a points increase would be. However, I think that we might end up giving up one of the abilities that WW grant; either the halving of the opponents weapons skill or the removal of the benefits of a second hand weapon. If I had to choose, I'd rather give up the former than the latter. If they nerf our invulnerable save, Wyches will become a lot less effective and maybe not even worth the points. After all, their T and S are still quite low for elite assault choices.
I almost guarantee that we're going to take a hit on the cost of our warriors. They cost the same as a regular CWE, but have better WS, BS and I. Also, I'll take one of our Succubi over a Warlock any day of the week. I've prepared myself to accept a points increase here.
Mandrakes should be a simple fix. Give them furious charge and possibly gruesome talismans and allow them to be led by a character with access to the armory. The concern about having Mandrake characters carrying an invulnerable WWP can be easily and fluffily addressed. In fluff, I've seen Mandrakes portrayed as skulking assassin types who have few compunctions about preying on other (dark) eldar. This would probably make them objects of suspicion and fear (more than ordinary) in DE society. What reasonably intelligent commander would trust such scoundrels to carry an item that decides whether or not and when the bulk of his elite forces arrived on the battlefield?
New rule:
Untrustworthy: Because of their reputation for preying on other DE, Mandrakes may not carry a WWP.
Grots could be easily fixed, too. Give them T5, save ++5, fleet and rending. (I know, most people don't like rending, but it makes sense and gives us a unit that can reliably damage tanks in assault.)
If GW made changes like that, it might actually become hard to decide whether to take Wyches, Grots or Mandrakes. Right now, it's pretty much a foregone conclusion.