OK, for starters, you’ll need heavily widened fender flares with lots of strakes…
It was fashionable to put the face of a sportier model on the tuned car as well, with the above link having at least two cars using different front fascia’s than stock.
More 80’s tuner pics
Bonus marks if you integrate a rear wing into the side strakes… You also will need a sunroof, IMO, as they massively amp up the cool factor!
The quality cars start with a red Scirocco and the best examples are at the bottom!
You’ll need multi-piece wheels and it helps if the centre is colour coded to the car’s paint colour. The outer rim should be either chrome or polished aluminium. You need to paint the car in a really striking colour; like bright red, blinding white, LEGO yellow or Bogliq blue!!!
The flares need to be boxy but look factory (assuming they took drugs first) unless the car was really rounded, like the Porsche 928 at the start of the forum thread in the third link… Look to tuned Golf and Scirocco GTi’s for inspiration since they tended to crib off of the factory hot rods style; only with the volume cranked to eleven!!!
I think your render is 90% there tbh; a sunroof, more rear flare (starting from the “B” pillar and ending at the back corner while also incorporating actual air intakes) plus a couple of spoilers (Above and below the rear window) and she’ll be a beast of uncommon beauty!