Thanks everyone, you all seem to be basically in agreement with me - I just hope my DM will agree ;)
One clarification though - according to the rules there is no need for a caster to make a spellcraft check to identify the spell being cast if they are using Dispel Magic:
Pg 208
Dispel Magic as a Counterspell: You can usually use dispel
magic to counterspell another spell being cast without
needing to identify the spell being cast.However, it would likely be a good idea to do so so that you don't end up blowing your Dispel Magic on a silly little cantrip.
Speaking as your DM, yes, I agree. We'll use Dispel Magic this way going forward. Thanks, everyone!