All of these are looking great! It's impressive you've taken (what I assume is) an identical character model and yet been able to get so many distinct-looking characters out of it. I love the look of VC7!

While he might not necessarily wear a crown... Vasudans seem to have the concept of armor. Maybe some kind of more ornate, ceremonial, "medieval" version of the armor you see on Vasudan pilots? Camera angle might add to the effect; a low angle might make him look impressive. I'll keep brainstorming...
Perhaps they only have 'functional' clothes that have a utility or symbolic meaning? So Vasudans don't have 'normal', 'fashion' clothes like we do, but have things like the flight suit (that might even heat their bodies while on Terran ships; if Vasudans are adapted for desert living, Terran temperatures might actually be a bit cold for them), armour, or thick robes for when there's sandstorms (reminded of Scroll of Atankharzim's robed vasudan). The scarf could thus maybe be a traditional symbol of office of some kind, allowed only by that specific caste or position (so not unlike a crown, but just they went with scarfs instead of headpieces)?