I own a 23 year old car (which you have seen!) it doesn't look like it from the outside with its shiny paint job etc but underneath it takes a lot of looking after. The previous owner gave me a booklet of around £7k worth of spend on parts in his 900 miles of ownership over 6 years. It was only on the strength of all the work done i.e. cambelt, pumps, hoses, clutch etc. that I bought the car. You just have to accept that some stuff on the car will fail due to age and you have to deal with it.
Inside I have tried to make the car more comfortable to live with but its still a 1995 car with its quirks. I think its worth just getting in the mindset that as you save up for that £500 nice exhaust its likely something like a water pump might fail and you spend the £500 on that instead.
All that said, I do secretly love the fact that my 23 year old car is as quick as most 2018 hot hatches but looks a lot cooler and is uber rare. Just driving a bit of rally history around gives me a huge buzz that no newer car could.