Is it worth getting a calcium score on a patient who is already on statin therapy?  

Plaque, usually TCFA (thin-capped fibroatheroma), benefits immensely from statin Rx. TCFAs are vulnerable plaques that are highly prone to rupture. The pleiotropic effects of statin Rx allow for plaque stabilization and reduce the vulnerability of the plaque to rupture. Calcification of plaque is a ...

Generally, not-someone on statins for a relatively short time (e.g. less than 3 years) who does not want to take medications might be reasonable. Longer-term statin use would typically not be useful unless there are major side effects, in which case, it might make more sense to change to another med...

No... unless the person was inappropriately prescribed a statin (was/is not statin eligible). An even in that case, you do not need a CAC score to stop the medication.