Yo! I rolled a Night Elf priest, and Starshards freakin rocks man. It has the most efficient mana to damage ratio out of all your spells. Better than anything Shadow has. Seriously, compare it to anything else, even Mind Flay.
http://db.vanillagaming.org/?search=starshards
Realistically, a fully fledged Shadow tree will be stronger than Starshards, but until you get there nothing beats it in efficiency, and ONLY because the Shadow tree gives so much +% shadow damage. Also the stun proc is really nifty. *BUT* Starshards gives those who might want to go Holy or Disc a really strong spell that is STRONGER than Shadow if the tree isn't touched at all.
Also NE get Shadowmeld, which should not be overlooked. You can camp rough spots in highly contested areas without much fear of getting ganked. Very useful in world and in PvP.
Haven't had a chance to try out Elune's Grace, but it looks OK. Where Fear Ward (Dwarf) is great against Warlocks and Priests, Elune's Grace is great against Hunters and decent against Rogues, Warriors and Shaman. Feedback (Human) looked OK, but any player worth their salt would just not cast on you during the duration. Desperate Prayer (Human, Dwarf) is probably better for PvP than Starshards.
In conclusion, each race has their advantages. Shadowmeld is amazing, and Starshards means you can still bring something to the fight without being Shadow. I haven't had a chance to try Elune's Grace yet, but it looks really strong against Hunters. Also +10% dodge chance is no joke, that's a 15 second 10% damage reduction to all non-spell attacks.
P.S. Cast bubble on yourself because it prevents interruption while taking damage, so you get your full 6 ticks each cast. It does NOT increase damage as time goes on like Curse of Agony, the ticks are the same damage throughout. When soloing I usually do Bubble Self > SW:Pain > Starshards x2 > Wand to finish. With Spirit Tap I have no downtime soloing.