I have long been an advocate for a slight flash nerf (another 15-30 sec CD) and a ghost buff to push the split between them to at least 25%/75%. Ghost, in theory, should be the option for champs who want to relentlessly chase like bruisers, tanks and even some ADC's. That just isn't the reality because Flash is far, FAR safer.
Ghost really needs changes that moves it closer to flash - something like this:
100% movespeed increase, lowering to 50% over 6 seconds. Damaging abilities or autoattacks within this time extend the duration to up to 10 seconds.
Simple change - and the 100% movespeed initially is to get that quick gap closer / escape, but still nowhere near as the instant flash. And so what if it is good on certain champions - perhaps give them adjusted changes or nerfs. This sort of chnage may break heca, rammus, singed but without looking at those champions too we can never get a decent Ghost.
EDIT: A downside of a good Ghost would be safe or late-game champs running both Flash and Ghost. Simple solution is to not allow both Flash and Ghost. Again it's not a perfect solution but at the moment our choices are "Flash and one other summoner" (of course with some exceptions such as Shaco or Heca), but it's much better than what we currently have.