Hi,
I would concur with the usefulness of it. I had in the past contemplated retrofitting it to my MK1 TT which can only take the basic sat nav but have given up with the idea. You only get turn instructions in the DIS and the routing doesn't seem to be that good at finding its way round complex road systems.
Regarding the double din and digital climate control, you could always consider retrofitting the digital climate control? Given that the dash would have to come out for a dash swap anyway, you would be a lot of the way there to getting to swap the manual control air system for one with electronic control. Although it would be more of a job to add the A/C compressor, heat exchanger and associated plumbing in the engine bay, without that you would still have electronically controlled thermostatic heating and ventilation. I'm not sure what the electronic climate control unit would think if the A/C compressor wasn't there. Whether its viable would depend on how much extra wiring is required as a minimum to make it operate and once the dash is off, how easy it would be to swap the main unit.
Just a thought.
regards
Andrew