I was going to type out a long army list review request but left the list at home. Basically the question settled down to how risky is it for a 5 game tourney to run with just the Slann as my only caster (I want to cut my skink priest to pay for my 5th terradon and magic items) I'm thinking lore of life is the best choice here for safety purposes.
You should still do ok. Where you are losing out is on the dispel scroll and the cube of darkness. If you did not have those items to start with, it should not matter too much. The slann is going to always be able to use up the casting dice.