Most cars are pretty reliable and well-made these days - especially the ones of German/Japanese design or manufacture (including those not necessarily built in Germany or Japan). Ask your dads about cars from 40-50 years ago! Mind you, it is annoying if you a re stuck with an annoying-hard-find-problem or a huge bill!
Popular, and smaller cars, especially the relatively simple ones, are really not that expensive to own and run - there's not much point picking on a model (which may have spanned many model versions) such as a Fiesta or Mini or Up or whatever and making a general statement about comparative reliability - reliability is now good enough for it to not be a factor for most people's buying decisions, even if all the cars in posts above have "quirks".
I'm just happy I bought the one I did (Citigo) - it's saving me a ton of money and it's great to drive.
As for cosmetic changes for 2021 on the GTi, most are minor and can often be altered if needs be. Or lived with. Cosmetic fiddling is a sure sign a car is in its twilight, so I'm just glad you can still buy them...
Cars are better made, and their construction and ability to resist the threat of dissolving under a light shower are sorted but from a mechanical standpoint, cars that get worthless pretty quickly on the other side of the graph have become more expensive to repair when you do get an issue. £1,800 for a clutch for example, which isn't even a problem as it's a wearable part.
As someone who has owned all 3 eras of BMW MINI and had good and bad ones, you cannot lump them in with the Up. The Up was designed as a cheap car to be spread across three marques, whereas the MINI shaped the premium small car cash-cow segment where everything was an option. My current Cooper S had a list price of £28,500 which is double that of a first edition Up GTI. They are complex cars with powerplants derived from those in the BMW 328 of the recently deceased generation, and I have been very specific about the eras of the cars I'm talking about.
As such, someone who buys my MINI at 4 years old can often be stung with horrendous engine and mechanical bills. An entry level Up or Mii might have nice running and repair costs, but I assure you - a MINI does not.
And as for German designed cars. I don't think a lot of them are mechanically anything to write home about even when their built in Germany. Mercs over the last 5 years, for example. Then you have cars built in the depths of Eastern Europe under French designs sporting Japanese badges which are predictably built like paper planes.
All the grease monkeys I know, even those in the first flush of youth, seem to be of the opinion that the oily bits of cars are made pretty shonkily next to some of the better stuff from 30 years ago, almost with built-in obsolescence.
I would still rather go new than old as cars have become fairly disposable, but I would tred very carefully when picking anything older that was anything more than a budget car when new - or something, such as an MX-5, that has a reputation for being not only relatively well built when new, but also cheap to fix.
I love the Mk 8 Fiesta ST, but I don't think I'd like to run one at five years old, next to a Mk 7 one with its fairly rudimentary mechanicals. But don't get me wrong, I prefer the newer car in every sense, and I'll only ever be running it from new - but you'll get the smelly end of stick at some point.
I had this conversation with someone at my work who bought a used E-class two years ago from a Merc dealer. I told him at the time. He's just had a £5,200 repair bill on a car probably not worth £14,000. I didn't want to say I told him so, obviously
But I did.
For him, there'll be 10 people who have a trouble-free experience in the same situation. But just don't be blind to the potential. I was. On balance, it's still probably cheaper but you'll just have the odd bump along the way, and sometimes they are quite painful. I just don't want them, so I'm prepared to pay more but always know what I'm paying. I'm also gradually reducing what I'm looking at buying, so reducing my costs that way - but that's just becoming an old fart, I suppose. Horses for courses, as they say at the French lasagne company.