I stretched to afford the GTI, though I was putting money aside that in a year or two I'd be able to buy one outright in cash. Instead, the right thing came up at the right time, and with what I had saved up I was able to put a down payment on it and keep my monthly reasonable. Now I'm ~2.5 years ahead of my loan and about to pay it off. I'm pretty sure I've modified every car I've ever owned, but I don't think I've ever explicitly planned for the cost of mods. I did plan to buy lighting upgrades for mine, just because the reflectors are awful.
I agree though, keeping cars long term saves a bunch of money, particularly if you DIY the maintenance. Even the smallest things like wipers, washing, and rotating your tires, is easy money.