Forgive me if I'm wrong, but can't you only use a wand if A) you have the spell it contains on your spell list or B) you have Use Magic Item, which has a chance for failure?
If I'm wrong about this, then let them be addicted to their healing wand. It'll run out of charges eventually, and using it in combat makes a character give up an action that could have been spent smiting the enemy.
General strategy - keep them from resting. If they leave to rest, have traps reset and reinforcements arrived. If they stay and rest, they are attacked in waves through the night. Make them try to get through entire dungeons in one go - spell use becomes a real problem for them then.
Kobolds and other intelligent class-capable monsters are considered races in my campaign, and character classes are as common among them as they are in PHB-race society. What's to keep a kobold Sor 3/Rog 1 from doing some nasty damage with invisibility + true strike + sneak attack? Then they get away with Expedious Retreat.
Use their own tactics against them. Attack them with spellcasters. See how the party defeats them. Have your next group of spellcasters try those same tactics against the party.
Give enemy groups a lacky (hasted would be best) with a wand of healing. When the PCs finally get it, it only has 2 charges left.
I'm a big fan of pits with oozes/green slime at the bottom - especially if the pit is deep and the cover shuts itself automatically. Usually the character survives - barely - but much valued equipment is lost.
Use traps with tripwires set just above kobold head height off the ground. The kobolds run away full tilt, the party goes after them, and that's when the flaming oil sqirts out of the walls and the portculli slam shut in front and behind...
Do the kobolds have an alchemist? Those tanglefoot bags are more trouble to PCs than they would seem at first glance...
Have kobold archers ready actions to fire poisoned arrows at people who start casting a spell. Make it STR-draining poison. Or any poison, really. Without a cleric, those ability scores heal slowly.
Be a Rat Bastard DM! Honestly TRY to kill the PCs. They can usually find a way to live, but let them worry about that little detail themselves.
etc...