The thing about dnd is that danger isn't about the constant drain on a party's resources, its about the critical moments.
I get hit loads of times, and they all take hp away, but I'm not sweating it till that there's the chance this hit will put me under.
Fireballs are nasty, but at higher levels will probably just weaken me. But that finger of death could end it here and now.
Sure, in general the elf's +2 dex will be better from avoiding attacks, and in the long run I will save much more damage. But what do I care, healing is cheap. As long as I live through the battle, I can use CLW wands or my buddy bandaid cleric. But its those moments where, crap this hit will kill me, where the elans ability becomes so incredibly powerful.
the big thing is that the +2 dex MIGHT prevent me from dying, the elan's ability WILL. The ability to consciously say, no I don't want this to happen, is so precious in dnd that it can not be underestimated.