If you can Claim Resources from your Properties, thanks to the Appraisers, it doesn’t help you to find very Special Resources and Special Items, required for the Quests to be completed. For this, you use the Explorers.
Special Items can include Ancient Maps, Lost Relics, Forgotten Manuscripts containing Forbidden Rituals, etc. These Items are required to break the Seals and recover the Lost Continents.
Special Resources are mainly non-material Resources (Power, Faith, Happiness, this kind of Resources). These Resources will be used too in the main Storyline, to compete with hidden Organizations or control them. No, I didn’t say Illuminati. No, I never said that. They don’t exist. Just build and mind your business. ^^