The spotlight rate's negligible. The most notable times it's worked for me were Halloween (got two Apple of Sodoms and Lantana, and a random Justicia) and Christmas (Christmas Rose and Poinsettia).

Just now, I did ten single rolls (four NG, six FG) and got four golds... and all of them were dupes. Three of them from fucking launch (Convallaria, Scarlet Tulip, Violet), the last one being my stalker, Cyrtanthus (who I swear I've gotten 10+ of by now).