Most of my favourite cameras are older than I am...
My Dad bought a new K2 in about 1978, I turned up four years later and bought my own K1000 in 1996 or so. Judging by the serial number I think it's probably from about 1979, really doesn't look its age! Still got it, haven't used it for ages (as frankly with KX/K2/MX to pick from when I want something hefty and mechanical why would I?)
The other desirable one from that original series is the 120mm f2.8, if you can find one. Goes from slightly soft wide open to sharp enough for architecture when you get down a couple of stops, thanks to the focal length you can shoot at 1/125 without shake and f2.8 gives you a bright viewfinder to work with. I had mine out today on a black ME with matching winder (the first generation one with six AAs) which fits the hand beautifully.
What I did think about (as I was doing my usual drive to a beauty spot, hop out, take photos) was that if I was trying to get a bit further down the paths than others bother to go I'd want to take a prime just for the reduced weight! To get the same image quality as the K 28mm f3.5 (my first choice for landscapes, very little distortion and sharp as they come) you'd need a pretty special zoom, which invariably means big and heavy.