Disclaimer: These suggestions are in no way complaints about the current version. I'd be happy to see them in the final version though.
1. At some point, abolish preparation cost / Kingdom gold altogether
I'm currently at the point where money doesn't really matter anymore -- all available upgrades bought, all dungeons unlocked. Only one or two special mission left. With more than 7000 gold sitting in the bank, I really can't see myself doing anything for money. And if I did ~30 runs trying to beat some impossible dungeon losing ~200 preparation gold everytime, and finally drop under, say 500 gold, I'd simply do some grinding in a normal or easy dungeon. Yet the very thought of spending money make me cringe. That's not fun.
Although the full game will no doubt provide tons of more stuffs to buy, upgrade and prepare, the simple truth is: a) At one point kingdom money will have no other use than preparation. b) The pressure of grinding/preparation cost discourages the player from trying new race/class/preparation/dungeon combinations, especially weird and outlandish things that challenges common sense.
Preparation is a headache. And weird things are fun. Trying new things and dying in different ways are fun. Having to worry about the cost of dying, is not.
Therefore I humbly suggest that in the final version, at certain point of the game -- say, when all (or maybe 90% or something) of kingdom upgrades are done, and you have more than maybe 5000 or 10000 gold -- have an option/upgrade to abolish kingdom gold or preparation cost. Like, 10000 gold for the upgrade "Sustainable Economy" that fixes the preparation cost to 0.
Same logic applies to locker items -- but other players have indeed raised the concern and there's not much to add.
2. In-game Encyclopedia, of monsters, items, deities and everything
Nothing too special. Just an in-game encyclopedia/gallery/catalogue/handbook sort of thing that allows you to view monster stats, item properties, race and class descriptions, deity details, etc. anytime and anywhere you want.
It could be gradually unlockable, like revealing the complete stats of a monster requires killing them 100 times or something (3 or 4 times for bosses). Angering/Being punished by deities reveals the specific rule in the handbook. Beating a certain dungeon several times reveals some info like the enemy types it spawns, the special sub-dungeons and events, etc. etc..
Basically the majority of the contents, the more common stuffs, should all be cleared by the time the "building/expanding" stage of the game is done. The remaining stuffs should correspond nicely with the harder dungeons and challenges, providing some extra incentives for players to complete them. 'Cos you know, when players see a percentage, they want to see it at 100%.
Plus it'd be super helpful and provide a change in pace/a little break. Sure it's basically a not-so-complete in-game wiki, but it'd be really nice.
Anyway, that's my two cents! Now for dreaming, I wish there's kind of a customizable "misclick alert" menu in the game, so I won't die accidentally, or piss of Glowing Guardian when I forgot about something....that might be too spoon-feeding though. Players may soon ask for a regret button....