I've only watched SW. I haven't checked out ESB or ROTJ yet. I've heard that ESB is DVNR'ed worse than the NTSC gout. I think in general though SW is a step up in most areas. It has less DVNR and there is a bit more resolution so the starfields don't disappear or twinkle like crazy. Not sure about EE though.
A PAL decoder/comb would probably unlock more detail than what the s315 does for sure. I think it's comb filter is bascially the simplest and cheapest they could find. Have you had any luck capturing PAL RF via a NTSC player yet? I think my HF9G captures a cleaner signal than the s315.