Honestly they're really only valuable if your home airport has a Centurion lounge. As much as I love Centurion lounges (and have access to them), I find myself in PP far more frequently.
Yeah, and if they're in the terminal you frequent too >.< At SFO, only T-I/T-3 (where the Centurion is) and T1-/T2 are connected airside. That said, I used to route everywhere via DFW so I could break the journey up and chill at the D17 lounge.