If Sam and Dean weren't brothers, I'd be less interested, but probably ship them. Because if it was proper non-incest (none of that half-assed; "Oh, we're secretly not related, so now we can have sex! The lifetime of shared experiences and thinking we're family don't matter!" crap), I think it would work beautifully as a big gay love story. But there would also be less of the interesting complications of them being family; Dean's "Winchesters against the world," attitude wouldn't be the same, Sam's conflict between normality and his family obviously wouldn't work, and a whole bunch of stuff that holds them together, but allows for unpleasantness to fester beneath the surface would just not be the same.

As is, I'm quite happy having them have intense brotherly love, and never have sex (except in twisted fanfic, purely for the purposes of watching the ensuing horrible psychological fallout).