Interesting turn this thread has taken. To pull off a restoration a vehicle 50-60-70 years has a very loose sliding scale of difficulty and expense and depends on so many things both seen and unseen at the start of the project its mind and sometimes budget blowing. Thats why so many people start out a restoration get half ways through it and run out of steam and have what I call a "stuck build", lots of those out there. Will one get there money back, sort of like getting interest on the sweat equity, totally depends on the amount of effort and money plowed into the build, the interest at the time for certain vehicles and the economy. More on this last line, a good and true build is a way easier sell then some POS bubba backyard project and forget about sending bubba dream restore to Barret Jackson. Certain vehicles are HOT then die out as there want/must have factor dies down, remember HUMVEEs where the MUST HAVE during Gulf I and into the 1990s till the price of gas cooled that which leads to the economy. Back in 2008 when the economy tanked and everybody in the US was out of work, Ebay was flooded with jeeps at reasonable prices. Jeep prices had a bubble after Saving Pte Ryan and Band of Bros everybody wanted one. Jeep owner gets laid off and has to make the call, keep a 10-15K vehicle in the drive or make the mortage payment, feed the family, etc.
Some vehicles hold there value regadless of the all the above factors but are limited by the number of potential purchasers, not just everybody can swing owning a tank, halftrack, or something exotic from overseas.