Practical Classics mag (I think) has a section where it gives a mini review of each make and model of old cars giving you a typical cost, performance, economy, but more importantly availability of mechanicals and bodywork.
MGs and Aircooled VWs have just about every nut and bolt available, remanufactured or improved, so some of the imconviences of older cars can be ironed out (and probably will have been by previous owners), with others though you might struggle to keep the car on the road routinely if you are constantly on the hunt for spares and service items.
The main issue with anything 30 years old, or even 10 years old…. have you looked at new cars recently? Go into say a Peugeot a show room and open all the doors on one of their cars, look at the thickness of the sills, and pillars, the big triangulated braces around the bases of the doors. New cars are tanks, heavy and rock solid, now look at all the pics that have been posted, with their lovely slender pillars and panoramic glass. That golf will weigh as much as any car it passes on the roads today. These days in an old car you are the crumple zone.
I used to drive an old MG, and it is great fun, the savings in tax and insurance though are insignificant, if you are driving daily then although parts and servicing can be cheap, the wait to get stuff, usually by mail order, means you can be off the road for a week or more for work that would be an afternoon with something more contemporary. I don't own a car at the moment, but if I was to buy one self preservation would lead me to the newest car my money can buy, not the oldest.