The obvious problem is you don't know how hard the vintage amp has been driven. If you have the time to look for one and enjoy the gamble, it is certainly possible to find a great deal for a song. However, I have always felt insecure about the vintage gear I have bought. At twenty plus years old, the electronics are not what they originally were.
If you are after the look, Yamaha has a series of nice amplifiers which look like units from the 1970's with MSRP ranging from $400 to $8,000:
http://usa.yamaha.com/products/audio-visual/hifi-components/amps/#page=1&mode=paging
I'm not sure all of them have phono preamps.
Some models also have the classic Yamaha Loudness knob.
My A-S700 has both and is a nice amp.