But it also doesn't touch her early game.
You're absolutely right that it affects her late-game. Shifting her base (0.658) by 0.01 would mean that she needs +386% AS to cap, instead of +380%. Shifting it down to 0.625 would mean she'd need +400% AS to hit the cap.
Well, minus her growth stat's +68%.
To have the same effective amount of change as reducing her base to 0.625, you could reduce her growth AS to +2.82% (caps at +48%), but that still makes absolutely no dent in her early-game, and offsets her attack speed by -0.132 at level 18 (this being the point where she either has enough attack speed that it does not matter or she has been shut down and does not matter).
From what I understand, both would nerf her late-game, but only one would also affect her early-game.
Alternatively, we could not focus on her base stats, because they're not so much of a problem.
Now, this is just my opinion, but I believe the two biggest problems with Vayne are the absolute superiority of BotRK for damage output--being the only on-hit item legitimately able to out-damage Crits--and Silver Bolts' flat damage that only serves to punish squishy targets more than tanks.