so far i have seen only zana's inventory rest to depend on weather you succeeded with daily or not.
other masters get it reset daily so i dont see the point in doing their missions past lvl8 unless you want to try your luck with item drops.
i've seen uniqs to drop in their missions but most of the time from tora/zana/caterina/vorici's as their missions send you to mini zones with monsters inside and since more you kill better chance to drop something useful.
you can check here what zone lvl you may expect based on the master's lvl
https://pathofexile.gamepedia.com/Master_Reputation_and_Favour
ps master's missions are good xp farm too. especially if you do full clear on the maps