The extraordinary ability low-light vision is a mess...
The elf racial trait low-light vision says
An elf can see twice as far as a human in starlight, moonlight, torchlight, and similar conditions of poor illumination. (PH 16)
The Player's Handbook on Vision and Light adds that one should
Double the effective radius of bright light and of shadowy illumination for such characters [that possess low-light vision]. (165)
The Monster Manual provides a similar description of low-light vision that's slightly more explicit:
A creature with low-light vision can see twice as far as a human in starlight, moonlight, torchlight, and similar conditions of shadowy illumination. (311)
And the Dungeon Master's Guide provides a description of low-light vision:
Characters with low-light vision have eyes that are so sensitive to light that they can see twice as far as normal in dim light. [...] Characters with low-light vision can see outdoors on a moonlit night as well as they can during the day.
Finally, the Rules Compendium provides another description of low-light vision:
Creatures that have low-light vision can see twice as far as normal in dim light. ... Those that have low-light vision can see outdoors on a moonlit night as well as a human can during the day. (115)
In other words: Yuck, or Ask the DM.
...But you can probably safely just take the best parts
The light levels poor and dim aren't listed Table 9–7: Light Sources and Illumination (PH 165), but shadowy totally is. And while torchlight can be either shadowy or bright illumination according to the same table, moonlight and starlight aren't even on the table.
So from the Player's Handbook section on Vision and Light take double the effective radius of bright light and shadowy illumination, from the Monster Manual description take starlight, and from the Dungeon Master's Guide description take see outdoors on a moonlit night as well as they can during the day. Put them in a Word Blender. Pour out...
Low-light Vision (Ex): A creature with low-light vision can see twice as far in bright and shadowy illumination. It can see outdoors on a starlit or moonlit night as well as a human can during the day.
When the torches go out (or whenever the DM says the night's overcast), such a creature is still blind, which is the rather severe downside of low-light vision. (I'm not sure discussing low-light vision with regards to flaws is entirely fair, given that one can always mitigate one's flaws simply by playing differently.)
"But how far can a human see in moonlight?"
Effectively, creatures can see as far as one of us humans actually can... that is, until the creature needs to use the skill Spot to determine the location of enemies.
The skill Spot isn't used to determine the literal distance a creature can see but how far away a creature can detect enemies. Each terrain has a Stealth and Detection entry that's used when determining the distance at which encounters effectively begin. For example, Stealth and Detection in a Forest says
In a sparse forest, the maximum distance at which a Spot check for detecting the nearby presence of others can succeed is 3d6×10 feet. In a medium forest, this distance is 2d8×10 feet, and in a dense forest it is 2d6×10 feet. (DMG 87)
So the DM determines the distance randomly. Then according to the skill Spot
The Dungeon Master may call for Spot checks to determine the distance at which an encounter begins. A penalty applies on such checks, depending on the distance between the two individuals or groups [a −1 penalty per 10 ft.], and an additional penalty may apply if the character making the Spot check is distracted (not concentrating on being observant) [a −5 penalty]. (83)
But the DM needn't call for such Spot skill checks and just declare the encounter begins. Further, if one or more creatures are in shadowy illumination those creature have concealment and can use that to make Hide skill checks, probably substantially reducing the chances they'll be noticed by an unobservant sentry making a Spot skill check. If one or more creature is in darkness then I hope you like rules.
D&D 3.5 never says exactly how far folks can see. Instead, the game explains how far away folks can see the next pile of XP.
Interesting point regarding the description of darkvision on PHB p. 184. However, the Monster Manual on p. 9 says:
Darkvision
A monster with darkvision can see in the dark within a specific radius. The monster can see in dim light within the radius as if it were bright light, and in darkness as if it were dim light. The monster can't discern color in
darkness, only shades of gray. Many creatures that live underground have this special sense.
This definition matches the PHB definition on p. 20. Comparing the PHB p. 20 and MM p. 9 definitions on the one hand with the PHB p. 184 definitions on the other, the only part in discrepancy is the part about "see in dim light within the radius as if it were bright light." The omission from p. 184 is only that, an omission. It isn't a contradiction.
It's reasonable to conclude that by RAW darkvision is darkvision, and works the same for every creature, unless otherwise noted in the creature's description.
The description on PHB p. 184-185 was corrected in this errata, which says:
Darkvision (p. 185). The definition of darkvision here now matches the definition everywhere else in the game (6th printing).
In summary, the definition of darkvision listed on p. 20 of the PHB is correct, and the omission on p. 185 was corrected in errata.
Best Answer
I spent about an hour looking, but I can no longer find the article, interview, video, or tweet I'm looking for. However, I'm certain that at some point there was a discussion with the designers about how much a given PC race's vision type counted for balance, and the response was basically, "none at all." In other words, the game designers did not rank PC darkvision as being significantly more valuable than normal vision for balance purposes, and treated it as a flavor component of each race.
I know a lot of players disagree, probably because every player seems to have a self-sufficiency reflex. And the Darkvision spell seems anomalous until you realize that it's 2nd level because it's specifically for when the narrow uses of darkvision exactly come into play. It's the same reason Knock and Spider Climb are 2nd level. They're not needed all that often, but when they are they're very useful.
Keep in mind that if you're following the game's rules that complete darkness is dim light to a character with darkvision, then characters with darkvision wandering around without a light source is only slightly less stupid than it is for characters with normal vision (-5 to passive Perception and disadvantage on Perception rolls). Such a party is all but guaranteed to trip every trap in the dungeon, and tasks like reading are likely going to be flat out impossible unless the print is particularly large. Even a party of Dwarves should be using a light source in an unfamiliar tunnel. Though light sources can be seen by other creatures, sound is often a bigger giveaway about the presence of other creatures.
Bottom line is that, from a design perspective, it's apparently not worth very much. At that level, I would grant an additional language, vehicle proficiency, or tool proficiency. Alternately, you might grant perception advantage in certain circumstances (e.g., Dwarves and Rock Gnomes underground, Elves and Forest Gnomes in the wilderness, etc.).