Sneaking already reduces enemy vision angle. Currently, the higher your Sneak ability, the narrower the enemy's vision angle is, for detection. My only change was
1) eliminate the AP scaling, since it makes sneak worthless unless you fully spec into it
2) give it some damage scaling, to give combat incentive for leveling it
If 30% per rank isn't enough, it could be increased. Now that I think about it, the primary purpose of early points in Sneaking should be unlocking Sneaking-based Talents (such as reducing the cost or giving you full movement speed while sneaking), with the latter points finally making sneaking cost-effective as a damage multiplier in combat.
The problem with this is that it makes Sneaking worthless in combat until you hit higher ranks of it. Ideally, it would start out 'okay' and then get better and better the more you spec into it.
