On most cars the issue is that the excessive motion comes from wear and slop in the bushes, so when you fit a short shift, you wind up with less throw, but just as much play, which makes it feel horrible and causes you to miss gears. Always worth renewing the bushes etc before modifying the throw.
On the clio there is an additional issue that the gearbox is utter utter s**t and rushing the synchros causes them to fail fairly quickly. That said, I dont really believe that shift length is a huge contributor, if you bang it through the gears with no mechanical sympathy then an extra inch of lever travel wont save you IMHO.
The modified shifter turrets are used because the gearlever is in a stupid place, which is awkward to reach, especially with buckets and harnesses, so the PMS and megane shifter raise the ball up closer to the wheel and further back. As an aside, they also come with new bushes etc, so people tend to notice a reduction in lever travel, withough it actually being a 'short shift'
Like everything else in the car world, people take something thats 100k old and falling apart, replace it with a modified component and wax lyrical about the benefits, when most of them would have come from simply repairing or replacing what was there. Polybushes are probably the best example of this!
