Agreed that her powers issue was a "dropped the ball" element with Guinan. Her pose and readiness to fight Q clearly indicated that the writers had it in mind for her to be a MUCH more powerful character than she really turned out to be. Maybe they didn't want her to be a deus ex machina character where she could potentially bail the crew out of danger or something. Or they were just lazy and didn't develop the idea.
I always considered her and her species as very powerful in some ways, but they were a more passive species and only use their powers for self defence, while Q would use their powers for whatever they felt like.
Back in Time's Arrow, she was injured and needed Picard's help.... that's evidence that her species isn't immortal like the Q, nor can they wave their hands to fix problems.... but they live for a very long time and the Q show some level of concern towards their species for some reason which I would conclude stems from their species being able to thwart some of the Q's abilities in some manner.
Here's what Memory Alpha has to say about her species, which are dubbed as "Listeners" (sounds to me as passive):
El-Aurians were a humanoid species of "listeners" originating from the El-Aurian system. Data once speculated (going from appearances) that El-Aurians have an awareness that supersedes the normal flow of time and space......
..... El-Aurians pride themselves on being a race of listeners, and appear to have a form of limited empathic ability. Some have used this to help others, acting as advisors or confidants. A few have turned their talent to more dubious pursuits, becoming con men and tricksters, such as Martus Mazur, while Dr. Soran used his abilities to help bring his genocidal plan to re-enter the Nexus to fruition.....
..... Much of their seeming reticence comes from the El-Aurian racial character. They appear to be natural lore-keepers, and use their phenomenal lifespans and memories to collect the stories and life experiences of various sentient beings. They preserve this knowledge for their own kind, and only occasionally share it with non-El-Aurians. They are a highly personable and empathic race, and as such are very willing to help other sentients work out their problems. It is possible as an offshoot of their prodigious memories and mental facilities that El-Aurians are extraordinarily sensitive to the space-time continuum itself. In 2366, Guinan was able to perceive an alternate timeline which occurred because of a disruption in the starship Enterprise-C's history......
(It was unclear if Guinan's special abilities and perceptions in regard to time and her ability to perceive Q were completely the result of her lineage, or if they were an extra side effect of her experience with the Nexus. According to the recent novel The Buried Age, Guinan's abilities were due to the echo of her left within the Nexus. This concept originated in an unfilmed scene in the Generations screenplay.)
Externally, the El-Aurians are physically identical to Humans, in structure and even the range of racial phenotypes. The only significant physical difference between Humans and El-Aurians is in the aging process, as the extremely long-lived El-Aurian lifespan covers many centuries.
El-Aurian names typically have two syllables.
So there were three El-Aurians in the ST series.