I think it's overkill on a car with stock power output. Here is my experience:
stock 325 with 3.15 diff - no problems with traction
stock 325 with 3.46 diff - no problems with traction
supercharged 325 with 3.15 diff - still no problems with open diff. Turned the DSC off for spirited driving.
supercharged 330 with 3.46 diff - I'm glad I got the Quaife, even with the LSD it's tricky to get some traction.
My vote goes to used diff ($200) and DIY, it's pretty easy swap as long as you stay with the same input flange (I believe the 3.38 from a 330 automatic does).