I don't think any of the monster receivers or "iconic" vintage audio pieces will get cheaper in the near future, for several reasons:
1. Sites like AK help raise awareness and interest in them (increased demand).
2. Growth in incomes and Internet reach, etc... in developing countries like India and China will fuel demand for these things, even if the percentage of people interested is much less than 1 percent of the population. World population this year is estimated to breach the 7 billion mark. You don't need a very high percentage of them to be interested in these things, before current demand will outstrip supply, and push prices up. (Increased demand.)
3. Supply of such things continually decreases, due to accidents, shipping damage, house fires (not every unit is a Marantz 2270

), natural disasters (how much audio gear disappeared in the earthquake and tsunami in Japan?), units thrown out that aren't saved by an AK type, and which end up in landfill, etc... (Decreased supply.)
4. We are entering an inflationary era, when things denominated in US $ will increase in price, period.
5. Increased raw materials prices and greater awareness of man's impact on the environment mean greater recycling efforts. Politics and economics, as much as or more than the facts, mean these pressures will not decrease any time soon. We've read here recently how some of these recycling efforts are leading to destruction of desirable gear. (Decreased demand.)
Eventually, the people who remember and love these things (baby boomers) will die out. Eventually, improvements in digital sound technology will make them obsolete (perhaps, eventually...

). As production-technological changes make more and more of their discrete components unavailable, more units will become unrepairable, due to lack of "unobtanium" components. All our beloved audio gear will eventually become near-forgotten decorative oddities like spinning wheels and crank-type telephones... something that will only be occasionally seen in a museum, or perhaps only in pictures in an online museum.
But that is a l-o-n-g way away, yet. In the shorter term, prices on these things will most likely rise, for the reasons I mentioned above (and perhaps other reasons I haven't thought of).