Sapphire gems are almost entirely useless. I highly suggest a buff. If you had 3 of the top tier gem you would only gain 5% more healing power. Compare that to the loss of 16% haste for sacrificing haste rolls for sockets on 2 weapons. The gap between the comparison will only get worse when level 50 is released. As far as I know, there are not going to be more gem tiers in game, yet there is certain to be higher haste rolls on the level 50 dungeon weapons.
Furthermore, heroic and legendary weapons are difficult to come by, yet haste roll weapons are relatively easy. That makes running ASV and collecting remnants for crafted weapons a pointless endeavor, which in turn gives level 45 prophets nothing to do after they get their BT/RG robe completed.
I suggest that the top tier Sapphire gem should be around 20-25% of the healing power that a level 50 would have. My current healing power at 45 is 12330 with no Sapphires at all. I suspect a level 50, fully geared, would have about 14000 healing power. I would not trade 16-20% haste for anything less than 60% more healing power (combined with 3 top tier gems), considering the effort needed to get there.