While thieves’ tools aren’t much help with disarming a lever, they can be used – given at least 5 minutes – to swap the on and off positions of the lever.
If you can do this, you can almost certainly make the lever simply not do anything at all.
Disarm: The easiest way to handle a pressure plate is to find a suitably heavy object to weigh it down, thereby freeing a creature to step off of the plate safely. However, tearing out nearby flagstones – requiring at least 5 minutes – allows a character using thieves’ tools (or ball bearings) to prop up the plate so that it cannot be depressed anymore.
I would have thought that wedging it with pitons would also potentially work if done carefully.
Spring Mechanism
Lacking thieves’ tools, a character can attempt to break the object with an attack (referring to the damaging objects rule in the DMG), though if an attack deals insufficient damage to destroy the object then the spring mechanism triggers.
You are ruling out the potential of opening the object in some way that avoids the spring mechanism.
Encounter Design: One of the most iconic traps of D&D is the poison needle hidden in the lock of a treasure chest.
It's unfortunately also one of the silliest, because it's one-shot and traps people who
attempt to open the chest instead of people who succeed at it. It also doesn't hurt people who just walk around to the back of the chest and cut a hole in it.
Disarm: Flying or levitating often avoids a tripwire altogether, as most tripwires are placed low to the ground. Taking an action to attack a tripwire can trigger the trap at a safe distance. An Intelligence (Investigation) check may be necessary to deduce where a tripwire leads to; once that area is located then thieves’ tools can be used to safely end the tension on the tripwire without triggering the trap.
You're fixated on attacks when other actions would work just as well. Tying a piece of string around the tripwire should be effective and incredibly unlikely to trigger the trap unless it's intended to kill mice.
Magical Ward
A magical ward, like the glyph of warding spell, is a form of abjuration which triggers according to specifications defined by the spellcaster.
Trap Examples: any use of glyph of warding, fire-breathing statues, sphere of annihilation
Notice: A magical ward is almost invisible to the senses, though an Intelligence (Arcana or Investigation) check made as part of a thorough search – typically requiring at least 5 minutes – will discover barely perceptible glowing runes. If this check is made in pitch darkness it has advantage. Detect magic will always detect a magical ward as abjuration magic.
Disarm: Dispel magic cast at the appropriate level will disarm the magical ward. Depending on the individual ward, other means of disarming may be possible, such as dealing cold damage to a ward triggering a spell dealing fire damage. Thieves’ tools can’t disarm a magical ward.
Encounter Design: When used in moderation, magical wards can go a long way toward evoking a dungeon’s theme. It’s worthwhile to think of unique ways that characters can become aware of the trigger without detect magic and overcome it without resorting to dispel magic. If there’s a password or object to bypass the ward, consider which creatures in the dungeon know the password or possess such an object.
First: the positive. I like the "detecting magical runes is easier in darkness" bit.
However, this is probably the one that needs the most information, yet you've given it the least.
How does the spell detect creatures? Is it visually based? Where is it looking from? What specific thing is it keyed to attack? How good is it at seeing past disguises? Can it see in the dark? Can it detect creatures through solid impediments? You don't have to specify this stuff, but a DM needs to have thought it through.
Why can't thieves' tools disarm it? Is it really unreasonable to assume that there are mundane countermeasures to magic?
Example: A necromancer has inscribed a symbol of death on his spell book. The PCs are going to pilfer it because they're not high enough level to confront him directly, and having him unable to use his best spells twice is a pretty substantial weakening.
The spell triggers is "anybody but me looks at the book from within 17 feet and 5 inches".
Because the PCs are high level and have sufficient information gathering skills (or sufficient paranoia), they know the spellbook to be magically trapped, but they can't get specifics.
What can players actually do except stand 120 feet away from the book and cast dispel magic?
And the answer comes down to those questions above - how does the magic detect them and trigger: can the PCs turn off the lights and then simply pick up the book? Can they wear an evil necromancer disguise and pick up the book? Can they pre-emptively trigger the spell by making it think there is a target creature nearby without risking themselves (the spell just says "creatures" trigger it, so technically throwing a bug with compound eyes at the book should trigger it - and if the spell is visually cued, how does it tell if something is a creature)? Can they make their way to the book while pushing a pavise to hide behind? If they get close enough without triggering the symbol, can they deface the symbol and deactivate the magic? Or just shove the book into a box and close the box?
Answering those questions makes a magic trap something fun that you can use with abandon, instead of "magic traps suck, so only use them to make dispel magic a spell worth knowing"
