If you are speaking about having to change the whole upper dash mate, then i think you will find it is a lot more hassle than it is worth. For the sake of saving only £700-1200, i wouldnt even bother. I would hold on until a nicer one comes along eventually.
There is always a temptation for people who are looking to buy a particular car, that they will "impulse buy" the first one they see because of the fact they want that type of car so much. I know a lot of people who have done this and regretted it.
This car to me, personally, cries out that it has not been looked after. The problems that you know of and can see, could only be the beginning of it mate, you could end up with a complete dog of a car in a few months when mechanical expensive things start to go wrong. And the chances are if the car hasnt had time and TLC spent on it, then its not going to have seen much money thrown at it maintenance wise either.
The dash needs replacing, the sunroof sounds like it has had some sort of VERY strange damage, the brakes sound dodgy, and the bumper will cost a few hundred to fix too. If you are also contemplating replacing the airbag / steering wheel, then that could well cost the £1200+ alone alongside the rest of it !
I still think you should walk away. Just because its your favourite colour and has 19" wheels doesnt mean you should overlook the fact that its not a good example.
Hope this helps mate
Michael