homeforsummerit's unlikely to do any damage to the brand mainly because it's only being sold to Aston owners,
According to Autocar's site, it will be sold to the general public too. I could very much see the appeal of it if it was exclusive to Aston owners, but if it is made available to the general public, then it is essentially the £20k equivalent of a Ferrari baseball cap/keyring.
I also personally feel that Aston Martin should at least make one or two mechanical alterations to the car, even if it that meant doing something as simple as tuning the exhaust to make it sound a little more special.
I am a big fan of the idea of luxury superminis, but I feel if a company as exclusive as Aston decide to venture into this area of the market, they need to do something more ground-breaking than simply re-skinning a current supermini. If the badge is the only USP, then I think it will be to the detriment of the brand as a whole.