It's fine to include Nynaeve in a battle with the BA and Messy, because that's fitting with her character and adds 'spice' as you say. Graendal, however, was put in charge of such an unimaginative plot that it was just embarrassing for her character. After like a year and a half of carefully building up her power base in secret, of covering her tracks but striking in somewhat-effective ways (most notably in TAR when Rand was fighting Rahvin, but also her other manipulations and alliances), and of fooling Rand into thinking she was dead while inspiring such paranoia and worry in him that he does potentially the most jaw-droppingly awful thing he's ever done (balefiring the whole palace), that takes him to the brink of losing it and going over to the dark side... after all that, after she's in the perfect place to be used as a strategic gambit against Rand, who thinks her dead for certain, she gets shoved into a plot of 'attack Perrin with a bunch of shadowspawn, have an eye-rollingly stupid backup plan in Jaret Byar, and then have it insinuated that you're raped by Shaidar Haran as punishment'. Yeesh. I think the 'spice' she added was not worth this totally unimaginative treatment of her character.