Yes on autoexplore, it indeed misinterprets the player's ability to explore certain areas at certain times. I think this is due to enemies blocking tight passages and the algorithm seeing a wall, although it might perhaps be more involved than that. I've been ignoring it since it doesn't have a particularly big impact on play.
Hit rate is missing limb effect. I'm not sure if this is intentional or not. The main purpose of these numbers is to tell you which weapon type would be best to use, so I think the magnitudes are maybe not so important. It should give the correct value though.
Spacebar is meant to use whatever items you are holding, and this includes swinging your weapons at an empty tile. I can see why you might think this should have nothing happen, but there are instances where you would want to try attacking what you cannot see, when you are blind for instance or when there are invisible creatures around. I can't have nothing happen because then you could exploit it when trying to attack while blind, and I don't want to remove the ability to try to attack things you cannot physically see either.
I'm not sure why you think that most enemies have >5 on most resistances late in the game as this is completely false. As a matter of fact, armor starts carrying lots of negative protection values the further in the game you go, so elemental offensive stat affinities get even better. Defense is generally better than offense, although if you kill slowly you are more likely to get into long fights, which has various consequences. I think I would always pick offense personally.
The levels before the blob city are more interesting in the full version of the game, because there are more enemies, each of which has a unique ability. Some people struggle to make it to the blob city though, so I'm not sure there is room to make things particularly harder there. It also depends on what type of character you play. I think the mage has it pretty easy early on whereas the melee is more enjoyable (to me at least). As far as harder enemies appearing, they already do, though perhaps maybe they aren't hard enough (e.g. the snake demon, fire blob, and ghost on the first level, and champs/kings/etc varieties).
Thanks for the feedback.