Bret/Austin is the perfect example.
Punk/Undertaker at WM this year might work as well. Punk taking Undertaker to his limit and having people standing on their feet believing that he's actually gonna pull it off would do wonders for how big of a star people perceive him as, whereas if he went in and beat the streak, some might still perceive it as a bit overwhelming and hard to swallow. Very weird situation, but on some level I can see where it makes sense.
Imagine Wrestlemania 25 had the 1995 version of Shawn Michaels going up against the 2009 version of Undertaker. If he had come that close to ending the sport's greatest streak and just barely failed, it would have made people look at him as a much bigger star than winning the world title itself would have done (or just as much.)
If you threw Daniel Bryan in there with Brock Lesnar and had him last as an underdog for awhile and even had him manage to slap on a hold on Lesnar at one point that could make Lesnar tap out, that would do just as much for him as a victory would.
Winning also doesn't automatically guarantee that the guy will get more over or become a bigger star. Not if they don't buy the victory. Kidman beating Hogan in 2000 WCW didn't get him more over. Cody Rhodes going out there and defeating The Rock (or even John Cena) fairly would him no favors. No one would believe it.