That should be easy to fix, especially if you aren't concerned about not being a 100 point concourse car. First, epoxy the cracks w/ JB weld and sand smooth. Don't worry that the texture isn't matched, just get everything the same level and smooth. Then, use this
process to apply a layer of quality vinyl upholstery to restore the surface to show quality. Get one of the new faux leather vinyls which are as pliable as any cloth and it will lay on and conform very easily to that corrugated surface. You can leave off the closed cell foam base layer and just glue the vinyl to the plastic. Just be sure to lay the vinyl beginning at one end and form it progressively into the lows and over the highs. Don't stretch the vinyl into the lows or it will tend to pull out of them.