This thread is in response to a specific request.
Perhaps the easiest thing to do would be to whisk together a little olive, a little balsamic vingar (preferably aged or reduced) and a little kosher salt.
I can't give you exact measurements, since I always go by taste and appearance.
With spinach, you can always add some toasted pignoli or (if you eat meat) a LITTLE bacon/grease to the recipe. I've never tried the bacon personally (ovo-lacto for 2.5 years), but I prepare it for the family and they love it!