I don't really have an issue with cantrip-spam, but I can see where others might. So instead of adding rules restrictions like uses per day or concentration, how about an
anti-cantrip? I posted this in another (and probably unrelated) thread, so I'll copy it here.
DIFFLE'S DENIAL
Abjuration cantrip (Wizard)
Casting Time: 1 reaction
Range: 60 feet
Components: S
Duration: Instantaneous
You attempt to interrupt a creature in the process of casting a cantrip. If the creature is casting a 0-level spell, the cantrip fails and has no effect. Spells of 1st level or higher are not affected by this cantrip.
It's basically Counterspell, except it only works on cantrips. It wouldn't take much more elbow grease to create a version that would
dispel cantrips that have already been cast.