No, what I'm saying is a standard car is £20k and a car with idrive is £22k.
When you sell the (hypothetical) cars the standard car is worth £10k and the car with idrive is worth £11k. So the cost of having idrive over your period of ownership is £1k.
Will it make the car better to drive? Of course not. It won't accelerate harder, stop better or go round corners generating more g. Will it make the ownership experience nicer? Only you can answer that. For me, yes it is. I ordered my E92 without it and I regretted it. I won't order another car again without, what I consider to be a central part of a cars command experience (desperately searching for a non-poncy description and clearly failed) - its so much more than navigation.
It sounds to me like, regardless of what reasons are tabled, you aren't buying into that theory, so you've answered your own question. Threads like this generally degenerate into scrappy arguments, because you're looking to play devils advocate and be convinced, and the masses trying to convince you soon tire of having their posts shot down.
Gone but not forgotten:
325i M Sport (E92), Black Sapphire, Coral Red Dakota, 19" 225's, Seat Heating, 6FL and de-badge
Replaced by 6.2 litres of AMG powered C class.