To be honest I don't think it would make much, if any difference to CC if you were a PPRuNe member or not. In my opinion, the vast majority of CC are going to treat you in the same way regardless, provided you're not being a pain! As a commercial passenger and as an ID90 standby, I have found that most CC are happy to chat at the galleys provided you're not getting in the way at busy times or otherwise stopping them from doing their jobs. It's probably a welcome break for them too on long night sectors...
Most flight crew are well aware of PPRuNe so I guess that's the difference between the FC and CC regarding this site. As was said to me when doing my PPL, "most pilots like to talk about being pilots" and almost all are interested if you have an interest in flying and will chat away quite happily!
Just my £0.02.