The coupler can help make a big difference, especially if your stock coupler is worn and sloppy.
One thing to note, a short shifter alone isn't of much value, it's having the Wevo spring system that is. There is no spring in the stock system to push the shifter from the 1 - 2 plane, to the normal 3 - 4 plane. So, shifting from 5th to what you think is 4th, could go directly into 2nd without any resistance that you're used to on your Subaru shifter.
I very much recommend the Wevo classic short shifter because it not only has that extra spring to keep you from making a big mistake, but also has a lock-out to keep you from shifting into reverse...an even bigger mistake.
It's not cheap at all, but is one of the very best upgrades I made to my car. It could very well save you from grenading your motor, which is even less cheap.
Here's the link:
Wevo Shifter