Prismatic Rift is one of the most underestimated skills of Embermage. While Elemental Attunement is on the other spectre... because most people don't understand that the % elemental debuffs applies to MELEE RANGE AOE! And the only benefit they take is from the extended duration which is not really needed because you're spaming spells and constantly refreshing that timer.
You are a long range class, your doom is melee attacks that survive your spell barrage. When 1 of those attacks hits you it has a chance for the mob to be sent faraway again, meaning he has to survive spell barrage 2... while you stay put spaming your spells yawning.
This is like a passive Frost Phase that unlocks on Lv1, but instead of teleporting you away it teleports them away. I always put 1 point on it before I reach Estherian Enclave. You should too, specialy if you're playing Elite. While you kite mobs your effective DPS is 0. Its hard to outrun mobs that have same movespeed as you, not to mention you can't outrun burning skeletons on Act I.
So 1 point in it is mandatory, just like 1 point into Frost Phase is later on. Regardless of your Embermage build.
Regarding your unspent points its hard to suggest with no information where have you spent your other points, although you seem to be focusing on Ice.
If you're gonna go with Wand, Wand Chaos is great with Icy Blast. Thunder Locus is a good option as it benefits from Hailstorm which you use and you can make use as an effective tactic versus champs/bosses. At least 1 point into Frozen Fate is also nice for the added passive crowd control. Ice Prison is also important, but on Elite it dies too quickly.
If you decide to put points in Fire, Blazing Pillar(s) is great for charge generation as a 1 click forget skill. Immolation aura is also good if you have low %DR, but increase at 5 a time... and add the Fire Brand.
If anyone here plays melee classes there are plenty of champs that have a version of this special ability and it makes killing them...harder.
Most likely, you'll either get frustrated with elite because it's too hard, or you forget you even have prismatic rift because it never does anything.