+1, well said. exactly why i chose to do this.NO. You don't need this. It is something to kill time for cheap, obsessive, worry warts like me.
The theory is that you might fractionally extend the life of your turbo by keeping a tiny amount of oil, water, and fuel mix from making its way into your intake. You'll be fine with out doing this mod.
On the other hand if you believe that it does something significant, then YES, it will have the same benefits for someone w/ a stock WRX as it does for a modified one. So you should probably do it. Maybe.
Besides, if you don't do it and your turbo dies prematurely you will always wonder if it would have saved you.
Hope this helps, T.J.