Hi,
I have a PP as part of NatWest Black, I think I've used it about five times in the last year, so I would never consider paying for it - I find it most useful in the USA (I have KLM and BA top tiers) - it seems that most clubs accept a PP and it saves time moving terminals to find an appropriate airline-linked lounge.
Of course, it does provide additional choice - and the servisair lounge in LHR/T1 is so much quieter in the evenings.
S.