for insignias all armor insignias are merch - they are overriden by the vanguard bonus and as such lose their function, so no value. for war the only viable one is knights insignia, whilst for casters survivor and radiant are used. unsalvages you get them for 300-600g, so no big gains there, salvage costs 2k/use, so better check the rune/insignia value before salvaging, because you armor rune is now worth 25g, so you lost the 2k value of the salvage and the value of the blue item. runes and insignias are usually sold unsalvaged in pre and the kits sold separately since many ppl do already have their own kit and then won't pay the 2k for your use - ending in salv rune prices usually lower for the common ones.
also there are no purple armor drops in pre - just to keep the hopes low 
