Then you're not doing Nurgle right. Let's take your example of Plaguebearers. First, I wouldn't even recommend those since you specified "low model count" but let's roll with them. Let's say you do the skin in a lighter scheme than the normal green. Then you can use Carroburg Crimson or maybe Cassandora Yellow to shade the boils, thereby highlighting them without fuss. Their open bellies are very easy if you paint them with some nice intestine colour like purple or brown and then give them a layer of Blood For the Blood God. And if you did that, all that's left are the swords. Bam, done in like twelve paints.
And once you actually git decent, you can use colour transitions, especially on the bigger stuff like Plague Drones, Beasts and pic related.