Yeah, I agree with you, a Series I headunit is perfectly fine. (My VE Calais V is a series 1, and it came with factory sat nav, and roof mounted DVD player).
There is also nothing wrong with using a tablet, smartphone, or PI to do some heavy lifting in terms of media functions, and use the headunit as a dumb device.
There was absolutely nothing wrong with my Series 1 headunit unit. For me though, I want my interior to look as factory as possible. I just want things to work when I need them, and not have to remember to pack my Nexus10 every time I want to check traffic, nav to a customer, or pull out my phone to make a call.
In the end, I put my money where my mouth is and ponied up just over $3000 for my interior upgrade.
This is probably much much more than ANYONE would want to spend on an IQ conversion.
My saving grace was that I sold my Series I stuff for just over $2000, which made the IQ upgrade very cheap....
Again, this is not something that would be suitable for everyone, or maybe anyone.
Just putting some of my expensive experience out there so others hopefully learn from the mistakes that I have made (and save some coin in the process).
For me, I have absolutely no regrets in the upgrade. Again its not something that I would recommend for everyone, but it is something that I enjoy, which for me is all that matters.
As a side note :
I have been working on a Raspberri Pi (MATE desktop, mono, ELM329 connected to SW Can for 11Bit and 29Bit comms).
The Pi is connected to the AUX video input on the headunit, and I have some rudimentary steering wheel and headunit controls working (29Bit can button broadcasts enumerated as keyboard presses).
This means that i can use XBMC to play media, but more importantly I can display the same sort of stuff as dash command (actually I can display a lot more because I am dealing with raw CAN messages here).
The Pi is powered directly by the car, and is hidden in the glovebox. (So no messy windscreen mounts, no dangling cables, and no crap to get in my way).
Ohhh, and the Pi costs less than $50