Speaking as a DC fan who is only recently aware of the awesomeness of Steve (particularly thanks to the "One Perfect Moment" scans), I have to staunchly disagree that Steve works better as a symbol. As a symbol, he can be read as being the bland, white-bread, jingoistic, flag-waving, one-note character that anyone can dismiss or pervert to their own means.
But when you actually see STEVE ROGERS, the man himself... this is a man "with a voice that could command a god, and does," remember? He is a character who inspires and excites as a living, vital, breathing character of action and humanity, not some detached and abstract symbol. NO one else is like Steve. No one else can BE like Steve. Bucky is Bucky, and he's awesome, but he does not inspire anybody. And that's what Steve does, just as Superman inspires the DCU. They are the linchpins to the moral hearts of their respective universes.
What Steve gives the Marvel Universe is unique and essential to its collective soul, and his absence has only helped it fall even further into the crap-hole it's become.
As a symbol, he's been good for jack shit. They need the man. We need Steve Rogers.