If you don't think the Army of Northern Virginia winning a massive battle in PA would have given Lee gains...Not sure what else to say.
It would have many implications ranging from the (fairly) minor such as allowing the Confederates to live off Northern land for a change, raising morale and keeping his supply lines open, to the massive political implications of smashing a Union army right on Washington DC's doorstep. I mean, it is hard to overestimate Gettysburg's importance.