I had bushes fitted to my GT-four which made my car very rigid round corners and certainly felt the bumps and pot holes a lot more.

But i had all my bolts replaced and a lot of restoration work done to the car but NEVER had any problems with my driveshafts even with 350+BHP.

No ofence to your buddy (i had the same with my mechanic) their knowledge is limited and i think your find with a lot of standard mechys that when it comes to something other then the normal product their knowledge falls down to opinion rather then fact.

Personally i'd take it to a reputable aftermarket performance garage with knowledge and ask the same question. could always call Jam-sport and ask them.