I like the idea of casters rolling to determine how strong their spell effects are, but it does cause problems with AoEs. If a wizard uses Glitterdust, for example, all the monsters in the area get their own roll, so you'd likely have some pass and some fail. If it's just one roll by the caster, you'd start seeing every monster in the area blinded if he rolled well, or every monster totally fine if he rolled poorly. Doesn't feel right.
Yet the idea of someone in the very center of a burst avoiding all damage because they're particularly agile (Evasion + Rolled well on Reflex) feels right?
I'm not trying to support one side or the other here, just pointing out that what "feels right" is really just familiar and accepted rather than sensible.
In another system I play an agile defense does NOTHING against area effects because if you are in the AoE you are affected. No amount of dodging that doesn't get you out of the AoE can save you. That makes sense.
Evasion + High Reflex should take you out of the area to the nearest unaffected square assuming you're capable of moving that far, or it just shouldn't work.
I dropped a few hundred damage in area effects once and the GM didn't even try to justify the two guys who rolled well with Evasion surviving it. He joked that they hid in each other's shadows, because one explanation is as dumb as the next.
I don't really have a problem with Evasion + High Reflex working within an area effect, I just don't think it "feels right," and also don't think "doesn't feel right" is a valid criticism of a mechanic (Although I don't deny things SHOULD "feel" good as much as possible, it's usually a personal preference though).
Actually I think Area Effects should trigger saves (You are being attacked by a location) and Targeted effects should attack defenses (You are being attacked by a person), but that's adding a layer of complexity when you don't lose much going for simplicity.