To be honest, I'm not so sure Sony will go to paid network access. In fact, I think PSN being free has been part of the reason why the PS3 has a higher sales rate than the 360, and why it continues to out-sell the 360, outside of a few well-developed countries.
So, really, it seems to me that both strategies have been successful, and I see no reason for either to change Next Gen--though I guess some of that might be relative to how successful PLUS has been (I have no idea).
As far as LIVE being worth the price, that's entirely subjective, and there really is no point arguing over it. Some people love it, and are happy to pay it. Personally, I do most of my online gaming on the PC, and am definitely not going to pay for LIVE just for now-and-then access. In fact, that was one of the primary reasons I went with a PS3.
