Imho....The mk5 gti has as good as chance as any, and it is very easily argued a better chance than most of becoming a "classic" and therefore a disproportionately expensive "asset".
I look back at my 67 Cooper S (sold in 80) and 71 TR 6 (sold in 1990) 78 Karmann Beetle cabrio (sold 96) - all immaculate, and weep at what they are "worth" today!
When the TR was selling, I was looking at an e type Jag as a replacement...not a hope in hell nowadays!
Thing is, life gets in the way...mortgages, kids, kids uni etc.....
....And, where to store all your toys meanwhile? Even if (like most of us) you will need the funds locked up those assets to buy some grotty family car/holiday/property etc.
You'll need a dry, airy, secure barn or similar; even then I eventually returned to find my cabby covered in sh1te, from birds nesting in the eaves. I gave up, sold it.
So you'll need to keep loving your toy too...or use a commercial storage facility (£250 a month?)
Imho those that have invested time and money in their cars deserve whatever the market will stand.
However, the classic car "investment" thing has crashed before, and will do so again!
If my ed was low mileage and orig I'd be keeping that, but it's neither!