To be fair that golf is overpriced.. but may just tempt someone who is not quite in the know. Like i said you could pick up an used r32 for 20k add a bi-turbo for 10k and you have got a 550bhp supercar slayer for 30k approx... which would make a RS6 look like a pram. All hypothetically speaking ofcourse...
I wouldnt do it.. but i guess the temptation is there to have a car that would make others look a little stupid when they have paid much more for their cars.
The difference between the Scooby/Evos is that you just wouldnt expect it from a golf.... where as a Scooby or Evo would probably be plastered with stickers and go faster stripes etc. The Golf still has the respect value in my opinion.. where as the others dont, and are just exactly what they are.. a fast car. 
please, 10k for biturbo, aha...
What about transmission? Don't tell me it does not need work with 550 eager horsies ripping it apart.
And if you got DSG you have to make some work on it, as it has 400Nm limit.
Then you have cooling issues as well.
Then you definitely need breaks.
Then you need an exhaust because you do not want you turbos to melt (On HGP Golf there is a valve that opens up at higher revs and releases some of the exhaust gases directly into atmosphere just to get the pressure down).
