Should I focus on intelligence and endurance for spellcasters or intelligence and dexterity. I was going to throw down with intelligence every level and sometimes put a point in endurance or dexterity. Which is more useful. I played Avadon 1 but that was a different game.

In this game unlike Avernum or Geneforge missle weapons and magic has priority and melee is used for defense at best so it's wise to invest in Dexterity and Intelligence. Endurance is optional but more important is to avoid taking damage than surviving it. As Avadon was mostly influenced by Geneforge series which affected Spiderweb Software next titles as a whole including Avernum second trilogy they share some late-game mechanics. Area of effect or summoned followers are not to be ignored too.