Jarjar, As a glider pilot who went onto commercial flying I tend to disagree.
Some of the many benefits include.
-Stick & Rudder skills are well taught by the gliding fraternity. It will give the pilot a good insight into proper control use (esp those things you rest your feet on!).
-You actually do real stalls & spins and fly the aircraft in turns at slow speed (you can't afford to add 5kts for every one of your brothers/sisters etc).
-You would gain a good understanding of weather and knowledge of how to read what is happening.
-Airman ship & teamwork are also some of the valuable lessons taught along the way.
-Those teaching gliding tend to do it because they love it, not because they have a shiny CPL and instructor rating.
-Gliding Instructors (unlike many instructors) aren't chasing airline jobs each week.
-They also aren't chasing "Just one more flight" which equates to "a couple more $$ in my pocket".
-Relative costs are lower that equivalent powered hours.
On top of this the tailwheel time that would come if you were to go on to towing would be invaluable.
Back to the orig question. -I think with the PPL you may have to do all the Dual Sequences with exemptions on the Solo stuff (at least thats how it used to work in the RPPL & PPL days). You may require silver C & 300km or similar to achieve the exemption.