I can't see them replacing Ninja. That location would be too difficult to work with, IMO. And the ride is still in relatively good shape, and one of the few family rides at the park.
While I'd be a bit bummed at Viper leaving, that makes more sense. It rarely draws a crowd, a last of it's kind, the ride is bumpy, and the location would be much easier to work with in that it's a self-contained plot of land.
I do agree not only with a front gate refresh, but also more upgraded bathrooms, especially near the main entrance and plaza. And I definitely concur they really should install more flat rides. Excluding kiddie rides (and Drop of Doom), they literally only have seven (Crazanity, Swashbuckler, Buccanner, Flash, Lasso, Scrambler, Bumpers), and five of those are at least 40 years old.