Thank you everyone for your comments. I learn something with each posting - here, I tried several different techniques for increasing contrast:
Fiona, your suggestion on the new layer with overlay blending, varying the opacity was an interesting new option that I will use again. I think I can see how it might produce different results in different circumstances and seems like one that is the most adjustable. I also tried reapplying a bit stronger curves adjustment and finally, the straightforward brightness/contrast adjustment - all 3 produced similar results.
Thanks again, your comments were helpful.
- Paul