As for fitting a deep threat into this offense, it could work just fine. That deep threat needs to be a lot more than just a deep threat though. Desean Jackson and Mike Wallace have no place in this offense. They'd become what Moss was. The real need is a player with elite speed who can also run all the routes. They have to be able to do the comeback, the deep out, the deep in, etc. Basically, we need Branch, but faster. I think both Tate and Price have that kind of ability, which is one reason I don't think we'll see a high-round WR in the coming draft.
The only out I remember was the one to Moss in last year's Saints game that got picked off. It's such a money play for a lot of teams, though, so I'd love to see more of it. And I completely agree on Price. He's Branch's replacement, probably after one more season. All that remains to be seen is if Tate will ever be a true #2 WR or if somebody else will be needed.
After a full season of work, Tate, who I've defended vigorously defended on other boards for his overall contributions compared to his hypothetical predecessor (Aiken), still isn't running deep routes well enough and doesn't appear to be able to get open at all on any other routes. Not that I'm advocating dumping Tate yet, but I think we're shopping again for that spot this off-season.