First, be wary about asking dealer to replace the head unit. Yours is only two weeks old - a replacement won't be a new unit, it will be a reconditioned unit, and hence probably older than your original!
If you've only had the TT two weeks, has the Gala always been like this, or was it ok then suddenly stop? I too had a 1.8T Golf, and the difference in the Gala effect between the two cars made me think it wasn't doing much either. Particularly in a TTR, the Gala effect isn't pronounced enough and I'm forever fiddling with the knob (so to speak...).
So, if it's always been like this, get a passenger to listen closely to the speakers to listen for any change in volume... only if you're really, really certain there isn't any would I ask the dealer to change the head unit.
Another thought: I don't know if Gala adjusts the head unit output (ie the 'line'-level signal going to the Bose amp), or whether it adjusts the gain of the Bose amp? Or whether there's some clever stuff between the two. Eg, maybe the head unit recognises the speed signal, and displays the Gala boost, and tries to tell the Bose, but can't?