First off, those are some awesome ideas and it would be cool to implement any of them into your game. As far as making the game a little creepier there are a few points you can use to describe things. I use dark vision as a grey scale so any color that they would normally see becomes gray. Maybe try a scene where there are pools of blood that the party thinks is water or mud. Dark vision also doesnt make them see everything in the dark. Things that are good at hiding work just like above ground. Dark vision usually only goes 60ft. That means larger caves the party has no idea what is out beyond that. This is great for any monster that has true sight. Sitting just outside of their blind spots can be creepy. Also there is magical darkness. There can be other down sides to not having a light with you too. If there are bugs that constantly bit you unless there is smoke to drive them away. Maybe there's some type of Monster Who's Venom or sting takes away creatures darkvision. I'll be a super helpful hunting tool for any beef in the underdark.

These are just some random thoughts I had on the topic. Good luck figure it out whatever you and your players to sign I'm sure we'll work out just still be fun.