If we have proof that Iran is supplying the missiles, there's no substitute for sending Tehran an exploding Valentine. But the targets chosen should be training centers near the Iraqi border or facilities otherwise associated with Tehran's subversion efforts: Make it hurt, but spare Iran's regular military and infrastructure - for now.
Why? Because we need to continue to make every reasonable effort to show the people of Iran that we don't regard them as our enemies, only the regime that they themselves despise. Hit the guilty, not their victims.
My understanding is that there are plenty of targets in terms just of Revolutionary Guard bases in Western Iran. And the anti-regime elements in Iran generally hate the RG, albeit sometimes reserving a bit of sympathy for them as stupid, indoctrinated hicks.
Makes sense, I'd like to see us do it. Perhaps in conjunction with strikes on the political leadership.