It's been a long time since I studied chemistry, but doesn't the reaction which causes corrosion, eventually neutralize the corrosive agent? Or does it just catalyze oxidation? Or does it depend?
I ask, because if the former, then the amount of corrosion that a leaky set of capacitors can cause is limited, even if allowed to go to completion. In some cases this may damage a board beyond repair, but in other cases the board will be repairable, if someone is willing and able to trace the corroded components and bypass destroyed connections and/or replace parts which have completely lost pins. Of course, for the custom Apple chips, that latter option is not available except through cannibalism.
We're actually discussing the repair/refurbishment of logic boards here. The specific issue is that the surface mount electrolytic capacitors leak corrosive which can damage the logic board and surrounding components.
As far as I know, the analog boards do not have any components which will cause similar damage if left unattended for years. Well, the battery, of course, but that's not soldered down.
Very few folks would pay that these days. There's no telling what folks in the future will be willing to pay. There's actually reason to believe that the prices on these old things will fall. We may be seeing the maximum right now. It has to do with the collectors tending to be folks who had or wanted these machines when they were younger and going for a nostalgia fix by way of collecting. As those folks satisfy their craving, or age further and loose interest, there will not necessarily be a new crop of collectors coming along to boost the value. Of course the supply is constantly decreasing too....
Doing a good job of refurbishing these boards is at least a couple of hours of custom electronics repair, plus parts, equipment, shipping, consumables, etc. It's difficult to make it an affordable service. Phreakout manages it by (in my opinion) undercharging for his time.