couldn't have said it better myself. Tires, tires, tires. Then the rest. I ran the last of the tread off the Goodyear Eagles that came with the wheels from the PO, and they were a huge improvement over the stock touring rubber. And then I put on Continental Extreme Contact DW Summer tires, and THAT was a huge improvement over the Eagles. It isn't sexy, like you make your first stoplight turn and go "oh wow, check that out!" But hit your favorite cloverleaf and the ultimate grip of the car is obviously far ahead of where it was before.
I'll tell you something, at the track this car, bone stock but for the 18"s and good tires, surprised people. Both instructors for the day commented on it. It certainly had more grip than I was qualified to fully exploit. Yes it was a little slow out of low speed exits, but that's my fault for all my novice early apex moments. It's a momentum car, not a drag car. Having said that, among other novices in "better" and "faster" cars, this Golf was all heart, and got around cars that should have stomped it. Again, not because it's faster....my point is, even a Golf TDi has formidable capabilities few of us are trained well enough to exploit. I sucked as a novice, but I sucked a little less than the others, with the result that the TDI was "faster" that day than a 911, whose owner quickly learned to be terrified of his gas pedal, a Trans Am that couldn't turn to save its life, and a BRZ, which also had major problems getting power down on a slightly wet track through its dinky Prius tires.
So ya....I'm spending my money on track time for now. Maybe if I qualify for solo runs I'll begin thinking about mods agains. ;-)