Clearly, my preference is to use concise text labels, but I’m sure there are situations where using icons is clearly the better choice regardless. I expect those situations to be rare though.

It doesn’t have to be all or nothing and that sounds like the approach you are taking. For example, I’m looking at a Canon digital camera that uses very clear icons for most commands, but they still use text labels like MENU, FUNCTION SET, DISPLAY, and ISO. (Not sure why they are upper case.) I find it interesting that they explicitly label the ON/OFF button even though the affordance of that button is very clear.

Putting it all together (without knowledge of your specific labels), I recommend the following:

Use standard icons when you can.
Use icons when their meaning is clear (without thought or experimentation).
Use text for top commands that don’t have good icons.
Use passable icons for rarely used, advanced commands that users are likely to require documentation for anyway.
Use text labels for everything else.

I think this approach will give you the right tradeoff.