Skills should be worth at the least the exact cost or somewhat more than a creature with the ability. Doubled is a bit much, at least as a fix all for creature abilities on Permanents.
Yeah. 8 cost for Nymph's tears as a permanent skill seems a little OTT. I'd put it at 6.
I also agree that it should be at least the cost of a creature, so the creature isn't penalized, and removed from decks.
Right, because if you can use the creature's ability without the creature, aside from the creature's attacking power, it becomes mostly obsolete.
I would ignore the skills of Nymphs. The nymphs are not the best examples of balance.
Would 150% seem more on par?
That's what I said in my other post, that, very basically, 50% more than the original for casting cost seems about right, but that's just roughly since it's much more based on the ability itself.