Is Nightmare any diffrent from the normal setting but with extra gold?
Really one of the things that could use improvement to this game is AI. Harder AI that plays smarter that does not rely on cheating/extra gold to win.
Hard/Nightmare AI should be worryed about preventing deaths and look at opponnets level in comarison to it's own. As well as time on target (I.E. maximize time killing creeps, etc).
Better AI, would not only help people learn (for people who want to comp stomp or play single player before jumping online) but it also would then be more okay to throw them in as replacements when players disconnect etc.