Nothing does touch it in terms of looks I agree, and the M135i for eg is more expensive to run - but it is more refined and has a better cabin, and is obviously quicker. I don't want to change as I love GTI's, and this one is special, but 28 weeks - really?? Anyway, I'll stop moaning now as I'm boring myself! 
I'd say the beemer's looks grow on you a lot when you sign on the dotted line (ha!), and likewise the GTI starts to look less special (but then the GTI is the one with the heritage). This makes sense as owners of both cars will typically tend to see them in a better light than others will I think. That said if a requirement is you want people to notice the car then don't get the beemer cause its a sleeper!
However, the running costs there are no getting around. Its gonna be 30mpg in the M instead of 40mpg in the GTI, and the tyre costs are probably £750 ish for a full set, hopefully only every 2 years

Anyone know what the GTI tyre costs are? I imagine they are lower but the fronts need replacing slightly more often?
So I wouldn't worry about the looks, but the running costs should be properly considered I'd say. Insurance is up a little (insignificant), tax is the same.