As of now, Lulu isn't in the _best_ shape. She isn't even played in competitive. She has her niche of disabling assassins and the like, but her defensive power has been decreased quite a bit. It has been decreased so much that even the powerful nature of her abilities can't offset the nerfs. Lulu can be buffed in many ways, but most ideas may result in quite toxic gameplay. However, there is a change that I think would make Lulu much better but would not make her terrible to play against.
W - Whimsy
RATIO : [5% per 100 ability power] ⇒ 10% per 100 ability power
MOVEMENT SPEED DURATION : 3/3.25/3.5/3.75/4 seconds ⇒3/3.5/4/4.5/5 seconds
This is simply a revert of a previous nerf. This was when Lulu had much more power in her kit, but since she isn't that powerful anymore, I believe that this would be a great buff for her. It won't make Lulu any more annoying, and it will take Lulu out of the gutter.