Alworth, I've used that exact term "game-manager" to describe Leftwich's game. I like your analysis. I don't know if Matt Jones, or any new Jags WR's they bring in for that matter, will ever become regular 1000 yarders.
I agree, it's better to have a game winner at QB if a team wants to become dominant. For every Trent Dilfer there are probably at least double that of winning Super bowl QB's that are high octane passers. Then there are the game winner-game loser inconsistent QB's, like my favourite, the New York Giant's QB Eli Manning. I don't know whats better the Eli Manning type or a game manager like Leftwich. I do think Manning has a chance to become quite good though if he can overcome his eraticness.