Installing new firmware "shouldn't" wipe the HDD or alter VIM etc. There is a CD available to download now that will re-enable it.
The only firmwares that im aware of will wipe the drives are 1200, 2660 and any 3XXX firmware (if coming from a 2XXX firmware) as they repartition the drive.
The OEM Antenna is the Roof mounted one. I can get the part no. but im away with work at the moment and haven't got my laptop with me. If you ring a VW Dealer they should be able to tell you the P/no. and also order you one.
I'm not guaranteeing that it will be 5 secs for you but the longest i've had to wait is about 30 secs.
Oh right I have only seen it on A hardware with newer firmware, and not had it on my B and running 38xx (I dont have working POI but thats a different issue)
I know you know more about this than me Carl so must just be my limited experience of 3-4 units!
No worries mate
Not all units will display Regensburg which is why i think (but can't prove) it is also down to GPS hardware.
I have a Skoda LED (which is newer than a VW C LED) and i still get it even with 2844 firmware.