The Audi 50 led to the VW Polo, one size smaller than Golf. Same layout, similar styling, few parts in common. First year of Golf (Rabbit) was '74, first year of Audi 50 was '74 (Polo was not long after). They launched within a few months of each other, so it appears that these were co-developed by two teams, one at VW and one at Audi, who were talking to each other. But, we digress...
For the Nissans ... If the ...37 models are priced high just look at the earlier ...35 model. Same car, slightly different engine. The G3x sedans are far more plentiful but manual transmissions might be hard to find. I haven't driven either a 350Z, 370Z nor a G35, G37.
As for the muscle cars and pony cars, whatever you want to call them. They ride and turn and stop much better than they did in the old days. For the Chrysler models, I haven't driven a Challenger but I have driven a 300C SRT8. (They're all the same underneath.) The powertrain is still the high point, and it's really good. It will turn and stop, but don't expect any feedback from the steering. It's fairly numb and disconnected - not to the extent of a Prius, or any of the pickup trucks (which all have video-game steering feedback ... none), but it doesn't feel sporty. I've driven a S197 Mustang, and it's better, but still not great. Haven't driven a Camaro, or the S550 Mustang.
So, do you want power, or do you want feel? If what you really want is the "feel" of a sporty car, then it is hard to beat a Miata, S2000, or the Toyobaru twins. I know there are complaints about lack of power with the Toyota 86; in what world is a 200 hp car "underpowered"? Every car I've ever owned, including today, has been around half that or less! Also, Mazda intentionally kept the Miata a low-powered car ... because it means the driver has to work it a little, and has to be involved in the process, even at sane (lower) speeds. The Toyota 86 intentionally comes with tires having relatively low grip (same type that the Prius uses!) because the driver can get some sliding happening, and gets more involved in the driving process, even at relatively lower speeds.
Of course, the problem there, is no back seat (or a useless back seat). Enter Ford Focus ST, Golf GTI, Civic SI, etc.
I have a customer within driving distance of Deals Gap, and I often arrange for a late flight home so that I can have an extra day ripping around. For a long time, the best rental car for Deals Gap was a Ford Focus. A while back, I found something that topped it, and it's one you would never expect ... the newest Toyota Yaris iA sedan (not the Yaris hatch), otherwise known as Scion iA. What most people don't know, is that this is a next-generation Mazda 2 underneath. We actually never got the next-generation Mazda 2, only the first one. Mazda does chassis tuning well. I was really surprised by that car. It's light and nimble, good steering, comfortable enough. There is definitely not much power but it doesn't need it.