The simple answer is that without elemental precision you stand to miss 17% of the lightning bolts you cast. I can't recall if the numbers have been run previously or whether there's a link to someone who has already mathed out the exact difference in terms of mana gained per cast before and after this talent. Suffice it to say, I talent into it 2/3 (I have sufficient spirit that 2/3 is enough to hit cap my bolts) because the piece of mind that every bolt i cast will hit and will give me mana back makes it all too worthwhile.
Spec'ing into elemental precision is also a choice of not spec'ing into ancestral swiftness, so please keep this in mind. Not 100% of shaman agree 1 way or the other, but I would suggest if you choose to spec into elem prec. as I have, to enchant your boots with lavawalker to minimize the loss of passive movement speed.
However you look at it, your choice to spec into either of these is a reflection of you as a healer and your preferences. There are fights that favor one over the other, such as Deathwing reg and heroic are amazing for lightning bolt spamming for mana back. I got nearly a million mana back on my first DW HM kill from that alone. Hagara HM frost phases however, some might find the extra mobility and instant ghost wolf casts to be overwhelmingly more important and useful.
End of the day, try it for yourself and see how you like it. I prefer every bolt hitting every time, and don't miss the instant ghost wolf in DS.
Adding on to this.
There is only a 5% difference between lavawalker and ghost wolf (unglyphed). In DS Heroics, Lavawalker is probably better than instant ghost wolf.
Considering our current 4 piece gives SWG a 20% haste + 5 seconds buff only increases the benefit of lava walker. It is probably better to drop the 2 points in instant ghost wolf for something else.
Since well handled DS heroics allow for a decent amount of time to be spent casting lightning bolt's you might as well drop it into the hit talents to improve mana regen.