Not sure if you have a firm grasp on how the roulettes work. Aside from any "In Need" reward, you basically get rewarded for first time runs--be that your first time through, someone else's first time through, or the daily rewards. There are also weekly limits imposed as well in some cases (some items have a weekly limit, and there is a hard limit to what you can hold at any time).
The first time you ever run some things (or first time on a particular job) you will get a unique bonus--once earned it is gone forever.
In some instances, when someone else is new you get a unique reward for helping that new player---you only get that when a new player is present.
And so and so and so forth.
There are a lot of instances that don't have any whomping big rewards out there (run several guildhest roulettes back to back---you may get a big reward for your first daily run, and then it can go to pot after that). Some don't even give you any rewards at all on their own--so without any daily/first timer bonuses you essentially don't get anything. Just as an example, look at the Ifrit Trial by itself:
http://ffxiv.gamerescape.com/wiki/Th...rs_%28Trial%29
The trial itself is not showing any rewards for completion. You get rewards from conditions linked to how you came to do the trial:
Notice that the instances you mentioned are both in that same list: Bowl of Embers and then Sastasha. You got your once daily reward from doing Ifrit, and Sastasha is another instance that has no rewards of it's own--you have to be either completing it for quest reward, or getting a conditional reward through the DF rules (first timer bonus or Daily Roulette bonus). The once daily bonuses reset based on Japan time (roughly 11AM EST in the US).
Read the descriptions carefully when viewing what you are selecting in the Duty Finder. If it will be a restricted reward for your selection, the description should give a hint to that effect. Here is what is currently showing on my Leveling Roulette, because I didn't run it today:
Description
A dungeon or trial will be selected at random from among those you have unlocked. Successful completion will earn you far greater rewards.
*Bonus EXP and Gil will be awarded to compensate for the discrepancy between character and duty levels. A further percentage will then be added based on character level.
*The amount of bonus company seals awarded is determined by class/job level.
*Allagan tomestones are only awarded to level 50 characters.
*The standard reward for this duty roulette category and all related bonuses are available once per day. The "adventurer in need" reward is always available.
Information
Duty Type: Light Party Dungeons & Trials
Awards Obtainable: Daily
Main Scenario has some similar language, but because I ran it today it also states this:
Information
Duty Type:Full Party Dungeons
Awards Obtainable: Daily/
Reward Already Received
Notice the orange text---it actually is colored like that in the DF listing.