Agreed. I wanted an MTX, but in the end decided I wanted the bells and whistles of the GT more. In the past, you could squeak out a couple of more MPG from a manual transmission, but in modern ATX cars the computers and their fancy fuel management are sophisticated enough to have closed that gap.
I don't use the semi-manual mode, mostly because when I'm slowing down I'm looking for the clutch (obviously ATX doesn't have one). There are some schools who say in a MTX you should downshift through the gears when coming to a stop. I would usually shift down, but always have the clutch in while coasting to a stop - so it wasn't really downshifting through the gears, as much as being a gear I could accelerate from at that speed.
I always feel like trying to downshift the ATX in manual mode is awkward - the revs jump and the momentum change feels like someone just stomped on the brakes.