Levelling - Why would you not want it to get harder? I don't see the problem, even if it's a bit spiky at times, that's not a bad thing.
Cave-In's - These have been nerfed so many times in the past, they should be left as they are. You'll learn in time to listen and then run like hell. I manage to evade cave ins without too much hassle.
Unbalanced Items/Drops - I think it'd be easier to suggest a better balancing system for this if we knew how the system generates them.
Mana-Steal Monsters - So you're asking for the game to be really easy?
Intelligence Stat/Spirit Stat -Stats depend entirely on the class(es) you choose. usually at least one of them is unnecessary, usually the spirit stat, because that's most confined to the faith based classes.
Wizards DPS Skill (or lack thereof) - Dud, if anything magic users need to be bought in line with fighters. You can clear rooms SO fast with magic spraying, but it's not nearly that easy with combat.