That's kinda bassackwards, but yeah, exactly. It's not an ego thing, it's a reality thing. She really is somebody in that she draws thousands to hear about politics, and her word sways votes. Why do you think that is? And why on earth do you think it would be as powerful if she didn't run for pres?
Timing is everything.
So yeah, her risk of becoming a "nobody" by not running is a pretty real one, if you ask me, and it's why I have always thought the "we need her to stay in the role she has now" mindset was so inane. The role she has now is a fleeting thing, just like opportunity always is.
Actually, "inane" isn't quite the right word -- vain, maybe, in the sense of "empty" -- but the purpose of people who put that meme around is quite concrete. Sarah, they say (sotto voce), should just go away and let People Like Us, the truly anointed of the Party, run everything -- now, who's got "next"?
But you're right, that's the mentality that gave us Gerald Ford, Bob Dole, John McCain, and yes, George W. Bush, too. At least Bush turned out to be better than most -- although he was never "not" a member of the Yacht Club.