I have 2 lists that are very similar: Slann Starmaster (260) Skink Priest (80) x40 Saurus Warriors (360) x40 Skinks (200) x10 Skinks (60) Bastiladon (280) Stegadon (240) 1480/1500 OR Slann Starmaster (260) Skink Priest (80) Astrolith Bearer (160) x40 Saurus Warriors (360) x10 Skinks (200) x10 Skinks (60) Bastiladon (280) Stegadon (240) 1500/1500 The difference is taking x10 Skinks and an Astrolith Bearer instead of x40 Skinks and no Astrolith. Astrolith seems very useful, but 40 Skinks also sounds terrifying to deal with. Which list would you go for?
Hmmm... I think that's a tough choice that depends on the army you play against. With Skinks you have lots of attacks and wounds more, and more mobility. That's good against armies causing mortal wounds. With the Astrolith Bearer you are a bit less mobile (because you have to stay in range but do a lot more damage because those rerolls are awesome. And your Slann also casts better, but you are more easily snipeable. One good spell or ranged ability can kill the Astrolith and you lose all that bonus.
In my experience the Astrolith bearer is invaluable - he will make your casting rolls easy and grant crucial rerolls for the heavy hitting Bastiladon and Stegadon. The Lords of Space and Time ability will also mean the bearer can teleport to wherever you need him the most. 40 skinks are indeed powerful though - have you considered dropping the warriors altogether and using a pure skink list? If you're going to be taking 40 warriors, consider swapping out the Stegadon for a Scar-Veteran on Carnosaur (assuming you have one) and making him your general - his command ability used on your saurus horde will grant them extra attacks on a hit roll of 5 because of their horde bonus.