I find 2000 gems for a limited time skin a bit too expensive. 400 Gems for a new skin of mounts is acceptable, however, the RNG system indeed makes it feel like you just spent gems on one of the most tricky lottery systems available to mankind. Mayby the vending of mount skins on the Trading Post could be a solution (so that people can buy and sell mount skins like Weapon skins are being marketed). In general the skins are very appealing and worth the full 400 gems, though not being able to choose which skin you are paying for is really stopping lots of people from buying it it seems.