Wow I can't believe this thread exists here. Many junior observers here too from the comments, its good to see the sports popularity growing, even if the comments aren't on the money (eg. Rossi has no opportunity to return Yamaha, according to Yamaha).
I've been watching MotoGP since 2003, saw the rise and fall and rise again of Valentino, big fan, being Australian, my less enthusiastic countryman always say 'how can you like Rossi and not Stoner?', but Stoner really wasn't anyone to me until 2006/07 and by then I was heavily watching Rossi for 5 years, so I wasn't just going to switch over with the snap of a finger.
I would say the battles between Stoner and Lorenzo last year and this year, are nothing to the ones of 2007/08 between Rossi and Stoner, so I think the next few years won't be that great, CRTs aren't helping either.
There's plenty of potential talent in the future, and even right now in GP, but some of the older riders need to move on, and considering there isn't anywhere for him to go, I would have to add Rossi to that list, unless he could get a satellite Honda, that might be interesting, but there's no knowing if he'll keep going here, he's done his due, he'll likely be remembered as the greatest rider of all time (even more than Agostini, just), so any further achievements, even 1-2 more championships, wouldn't mean anything at this point (but he would still get paid, not that he'd need the money necessarily).