It would be quite nice to be able to say to all those players who left Rugby League because they'd 'won everything there was to win' - "Here's something you didn't win, and now never will."
Slightly more seriously, I think the spin-off for the British game would be immense. We can talk excitedly among ourselves about how well-balanced SL is and how it's great to watch competitive domestic matches, but out in the real world we are increasingly seen as a feeder sport for RU. Plus, I don't think it helps our status that our 'big brother - i.e. the Aussie game - doesn't give two hoots about us. Now they've got Origin, international RL could disappear tomorrow and they wouldn't care.
To win a major international tournament would turn all this around somewhat, certainly in terms of publicity. Okay, the Aussies would make their usual pile of churlish excuses, but they would be stung and may feel sufficiently challenged to help make the World Cup into a major event.
In short it could be just the boost we need, at just the right time.