So I have the common dual cracks in my dashboard for a 79 zx, are molded dashboard covers a good fix?

as long as you get a full cover and not a half i think they look pretty good. I have run into them in the wrecking yard after years of abuse and they look factory until you get up close to it. here is a pic of mine. i literally just tossed it on there because i needed to store it someplace and i figured the dash was a good spot. its not glued in and i made no attempt to make it fit nicely: https://sites.google.com/a/thecomputerrehab.com/260z/Interior/dash-cover

I've a ZX also, and it came with a full dash cap. Just as Kurby said, get a full one, not a half cap. I didn't even realize my dash had a cap, the color matched right, and it was fitted/adheared well... though I did notice some warping ahead of the speedo cluster.

Motorsport auto sells the covers : http://www.thezstore.com/page/TZS/PROD/DC/50-2023

though depending on how badly your dash is cracked, you might be able to repair it yourself-others have done so for not much money.

Yea that does look pretty good with the cover, thanks.