my opinion is that it does help the plants, yes. i also noticed that when i added a black background to my big tank (instead of the light reflecting off the white wall behind the tank) it got a little darker. environment definitely makes the difference.
50gal planted - yoyo loaches, BNs, odessa barbs, giant danios
33gal planted - praecox rainbows, gold ram, bolivian rams, sparkling gouramis, licorice gouramis, lots of shrimp
2 x 5gal planted - bettas