Strontium is difficult to detect because it is masked by calcium. At present, there are no reliable and practical kits for measuring strontium in a reef tank. NO i am not testing for it.
I'd say strontium gets depleted in a thriving stony reef tank as fast as magnesium does, if not more.
Salifert is a decent test kit but as you stated, you need to go through the calcium test portion first and that part is always off.
So yes, I do test for strontium and it's always lacking to the point that I just add on a weekly basis now.