The prices that the Marantz 22XX series of receivers from the 1970's command on auction sites like eBay have risen fairly dramatically in the last two years (up anywhere from 30 - 100%). The Marantz 22xx series have a fairly devoted following, complete with websites (www.classic-audio.com) and yahoo groups (MarantzTalk) devoted to these vintage units.
Supposedly each receiver had a fairly specific design goal. For example, certain units like the 2230 and 2270 are in comparatively higher demand, as these two units were designed to have an almost tube like sound to them. There is always the occasional thread as to whether or not the baby Marantz's (2215; 2216) had better FM tuners than the rest of the line. And so it goes. FYI, the 22XX series was for 2 channel; the 4XXX series was for quad; the XX stands for the watts per channel.
As far as looks go, these receivers are amongst the best looking of the 1970's solid state receivers. Tank like build; quality parts; solid aluminum, oversized faceplates; script lettering; gyro tuning; and of course, the blue lights ... which depending on the model ... was either against a black or silver backdrop.
The Marantz sound is warm, lush, and very musical. Lively preamps. They work well as tuners (I use a 2240 as a tuner in my main system) or as a power source in a secondary system (I use a 2216B for my bedroom system). Modern era speakers & CD players mate well with the Marantz receivers.
Of the vintage units, the Marantz 22XX series; the Yamaha CR series; the Fisher tube receivers from the 60's (400; 500;800) and the Pioneer SX and XXX (626/737/etc.) series probably represent the best of class. There are some sleepers out there ... the Sherwood 7100 & Advent 300 (outrageous tuners).
If you pick one up, expect some amount of cleaning/repair. Bill at Music Technologies in Springfield, VA and Mike Zuccaro in San Diego are amongst the best in restoring the Marantz receivers. The Soundsmith in Peekskill is good, as well.
Regards, Rich