Not sure if you've seen any of the videos that have circulated, but the created explosions was bigger than just getting a bruise on the waist from it. Seems it'd be enough to stand next to someone with one of those pagers to get hurt by it.
Probably because they have been stalking for a while, and this escalation is a precursor to further action. Destroying lines of communication is usually done before military action.
I think the "clever show" was the point. The physical damage may not actually justify the investment here. You need the resultant paranoia and suspicion from Hezbollah or it wasn't worth putting resources into.