I did a lot of thinking about this before I rolled mine. I think some believe Wood Elf because they have a high starting wisdom without taking TOO big a hit on their physical stats and many people who play mystics like to get into melee and mix it up, even if it is only timing aa's between casts. I also like the racial that improves power regen. In a less than ideal instance group this a goblin totem and your mana stone can mean shorter down time after had fights. Not as good as the constant of an Erudite but good enough.
I looked at it this way
Pure healer no melee mystics (why don't I roll a defiler then?

) Erudite.
"Battle Shaman" (why didn't you roll a berserker? Oh wait I already have one at 80

) Barbarian
Hybrid, wants to heal well and mix it up on occassion (can't you make up your mind? Nope) Wood elf
As you said though in the end it really doesn't matter. With the shard armor and/or the Crimson Robe even non-raiders can get pretty nicely reduced cast times, and the same itemization can make up for stat defficiencies. Ultimately it comes down to the "flavor" of the race. Heck if you aren't into lore and don't care what your toon looks like, put on a blind fold and click. <shrug>