As for exping: seems futile in the actual version 0.89b
Not only each 10 levels you get 1 less skill points to distribute.
Not only the power/efficiency of each skill you invest in, rises in a logarithmic way.
But AI heroes somehow perform much better, when they are generated based on your level.
(in other words, AI hero level 25 of similar class will always beat your hero on level 25, but this is not the case on lower levels, like 1~15)
It looks like the AI heroes still run on the old (arithmetical skill power increase), hence your hero will gradually grow weaker, while AI doesn't.
Also the Race Synergy Bonus of AI is a bit stronger than the new tweaked RCB of player heroes (Example: why Daemons now have 3 different RCBs, A) +5% to skills / sould, B) Implant a spy, C) build a tower, AI Daemon can still summon loads of Succubi, and they smartly use it when my hero closes in)
So more XP I get, more frustrated I am