Loot has always been Perfidus' draw. Malthor has the largest variety of potential loot on the server (or one of the largest, I don't have a large variety of info from Sithicus bosses yet!). Quite a few unique items that only drop from him, as far as my tracking and notes go. Sure, with that variety unfortunately comes a downpour of junk too, and sometimes you come up empty, but thats the downside of loot, in general.
Not saying they -shouldn't- add more, but rather then change up the cold varnishes, what about a change to the acid varnishes? I've always wondered why there are no greater acids... perhaps a change to the biles, make the bigger ones craft 3 biles --> 1 essense for greater acids. Puts more variety in the mix, rewards with higher end varnishes, and keeps Ice Palace in having a small purpose in having the better location for cold varnishes.
And its not -that- hard to find Perfidus. It usually took me 5-10 minutes of looking on Bree when I was bored. Occasionally took longer, and of course would take longer with a group if your clearing the Mists.. but that has its own rewards in the reagants.