First, I do not this this method has any boosted complication, I think it is exactly what is allowed within the RAW. I think your method is ridiculously strong, even if you allow a free perception roll every turn and a boosted perception roll whenever you are attacked. Basically, it allows any caster with spirit to escape any physical encounter (against all but the most perceptive opponents, and I cant think of many foes with apex perception skills), for virtually free. You never have to conceded, you just veil. Further, you can just vanish whenever something comes after you, and give them no recourse at all while you re-position/have tankier friends get in the way. One of the few weaknesses of wizards is that they are often squishy (at least without enchanted item charges), and this allows them to use 1 charge to soak a hit, then veil and jump behind the beefy people, the downside of the bad guy hitting someone else is not really a downside, since that is what you wanted anyway. This does not even take into account the fact that you can attack. Say you have a 6 shift veil, you are unlikely to be perceived, then you use some evocation attack, this is unlikely to grant more than a +2 bonus on the alertness check (if that) unless you make it obvious which direction it came from. The 3 shift block is likely not a factor since you can easily get more than 3 with Discipline, and their defense is likely more than 3. And then they can make no reprisal. It is pretty plainly broken.
Second, it is a block against perception, not a block against attacking at you. Sure they cant see where you are, but since in order to do any sort of attack they have to know you exist (any also which zone you are in, or at least guess), they almost certainly have a general idea. They saw where the snowball came from, or heard you make a noise, or whatever. Then they swing their giant club all your zone, or shoot 5 shots with their pistol into your general area. They don't have to hit you to inflict stress or even consequences, they just have to make you move quickly to avoid them, this could drain your physical reserves some (small stress), have you scrape yourself/stub your toe (larger stress), or twist your ankle (potentially a mild consequence). They do not have to cover a whole zone to inflict stress on you (though if they did with a zone attack I wouldn't even let your block apply), an attack roll from then high enough to beat your block implies either they got lucky and hit you, they got close and grazed you, or they made you move akwardly to avoid your clumsy but close swing.
Third, if they cannot attack (target) her at all, her block is certainly against their attacks. You cannot prevent them from attacking you in any way and then say that you are not blocking attacks. Being able to roll their full strength attack against a block does not mean their attack is fully effective, if it did they wouldn't be rolling against a block. Further, one could rule that the veil places an I'm Invisible aspect, that, at least once, can be tagged for a defense/to reduce an attack, so you get to do that too if you want. Further, the attack is not another chance to beat the block, it is not a boosted re-roll. Even if the attack were successful the block wouldn't fade, you get to keep it until they actually see you. This is a special feature of veils that makes them already more powerful defensively than any other block, since they are the only block that (at worst) functions as a block against attacks, and doesn't fade once pierced by an attack.