No, Nin, the game is not finished until you have maxed out your VR and Coins. And also if you want, you have to have world record times in all 32 courses ...
The gold kart is fine. I prefer it more than the standard kart as it adds additional speed and weight. Not much of a difference with the acceleration if I have my Shy Guy. As for the wheels, I'm not too happy with 'em.
All 3 Golden Parts can be achieved by either a certain amount of coins, OR another way.
Gold Glider:
Collect 10,000 coins
OR
Get 100 StreetPasses
Golden Wheels:
Collect 15,000 coins
OR
Get a minimum of 1 star ranking on every cup in Mario GP
Gold Standard:
Collect 20,000 coins
OR
Get 10,000 VR points.
Now, how far am I at getting Gold Parts?
I already have the Gold Wheels, but as of now: VR: 2059 (20.59% for Gold Standard) Coins: 6940 (69.40% for Gold Glider, and 34.70% for Gold Standard) StreetPasses: 8 (8% for Gold Glider)
Oh and for the sake of it: Wins: 610 Losses:699 Percentage: 46.6% wins, 53.4% losses
I have the Gold Wheels and the Gold Glider and I'm a little over halfway for the Gold Standard (VR wise).
Here are my stats: VR: 5297 Wins: 1755 Losses: 295 Coins Collected: 11797 Streetpass Tags: 86