Container traps’ effects scale based on dungeon level (ideally on the level a container generated, not on the current level, so a player can’t bring a chest up to level 1 to make it use the weakest possible trap.)

In addition to adding some more effects, also add some effects which cosmetically are the same as other ones, but are more or less damaging. This would, however, make untrapping containers even more useless than it is now; perhaps a trap should stay armed even after you set it off. Another idea is to give certain traps an arming item, like a potion of oil for the fire effect and a land mine for the explosion effect. Successfully untrapping it will deposit the arming item into the container.

Also, make container traps independent of Luck, because currently they encourage the player to ignore containers until Luck is maximized.

Kicking down doors exercises Str and not Dex.

Black pudding globs convey only one of the three intrinsics they currently convey (maybe shock resistance), and brown pudding globs convey another (maybe cold resistance).

More marginal corner-case uses for gems (similar to the amethyst/booze interaction):

• Throwing a diamond (or a diamond ring) at an opposite-sex foocubus will tame it.
• Rubbing an amber stone generates electricity, perhaps giving you a static charge that will add a bit of damage to your next melee attack.
• Hitting a demon with obsidian traps it as if it were a bear trap: it can’t move or teleport, though it can still attack. This also destroys the obsidian.
• Moonstone allows you to control lycanthropic shapeshifting. (Moonstone exists only as a ring in vanilla, not as a real gemstone.)
• Rubies and sapphires provide some very marginal protection against cold and fire respectively.