I got back into CB750s about 4 years ago. Since them I've seen prices increase dramatically for good parts. The junk parts will always sell at junk prices, but the good stuff has increased in quantum leaps.
This newfound interest in the old CBs has taken a lot of the "hobby" part out of it and made it more expensive to play.
However, I got back into the bikes again as the prices of cars went insane and televising things like Barrett-Jackson didn't help matters.
I couldn't play in the area of $2500 steering wheels, $7500 fenders, $2000 trunk lid finish panels. The bikes could still be had for seemingly decent coin. How far the march upwards continues - the market will decide.
As long as someone will pay the asking price, it will continue. And for each asking price received, the next guy says "Hummmm....wonder if I can get more......"