Vintage receivers???

The biggest problems with old Marantz receivers isn't the sound quality. It's the idiotic prices for the units and the time it takes to get work done on them. All that said, I discourage some models such as the 2270. That's a complicated receiver with complicated adjustments that are prone to drifting and it requires service every couple of years to keep it in spec. The mid and late 70's designs are less complicated. The 2230 is well regarded for it's tuner and phono section, often compared to the 2270, and it's simpler. 
Recapping them isn't hard. Some people make it more complicated than it is. It's not that hard. 

The prices over the last few years are most definitely not driven by the quality of sound you get from that old gear. It's an unusually long lived fad propelled primarily by millennials and hipsters raised on iTunes and earbuds who've never heard a decent stereo. I live right next door to a record shop that sells vintage gear. I've been shocked by the prices they ask for garbage that doesn't even have the right parts or working switches while they practically give away flawless higher end Adcom gear. It's insane. I saw them asking nearly a thousand dollars for a Marantz 250M that literally had a bag of spare parts sitting on top of it and the covers weren't even screwed on tight. It was gone in 2 weeks. 

I don’t have any trouble going through and doing some recapping and adjustment. It’s mandatory on this old stuff before you even plug it in. That’s why so much of it is dead or dies shortly after it used for the first time in a long time. Many of these old units used glue on the PCBs to hold parts on that corrodes into a substance that eats the legs and traces off components and circuit boards. Marantz is one that never used that crap. Sansui used it on everything. The best advice I can give if you want to get into opening these things up is just start simple. If you’re hellbent on doing the work, do it, then take it to a good CB radio tech for the alignment.

@minorl 
A 2252 definitely outdoes a 2252B. The '78+ B variants are half the receiver that '77 and prior units are. '77 is where I draw the hard line. I think they screwed the pooch when they started consolidating boards like they did on new '78 B variants. Not only that, it just made the things much harder to take apart. 

I’d say the 240 is a horrible choice if you’re looking for a unit to learn on. The gigantic caps in it aren’t cheap. It’s full of unobtanium transistors. And most importantly, you NEED a bench full of gear to properly adjust one. They’re prone to oscillating if not properly dialed in. I’ve read a few stories where experienced techs have dug into 200 series amps to do simple work and end up with 500mV at 250kHz on the outputs or something like that and no clue why.