Everything is worth "something", probably not much if they're just cores.
and yes they are rebuildable. I've seen both diy solutions that involve sanding, filling in cracks, bondo over Everything, then paint. Doesn't look factory but doesn't look bad
These guys do top notch restorations, a dart dash for them would be a walk in the park Classic Car Interior Restoration | Just Dashes
Jay Leno has vouched for them and applauded their work for what that is worth to you
I was walking to go give my core pads away at Spring Fling one year when a guy asked me what I was going to do with them. He offered me $20 each. SOLD. I had five or six at the time.