For Vision, Daylight and Bright Are The Same
For vision and hiding purposes, there are only three levels of light, as you mentioned. Bright, Shadowy, and Darkness.
"Bright" in this case means it's bright enough that there is no hindrance to vision at all. "Shadowy" grants concealment, and Darkness creates effective blindness if you can't mitigate it.
So yes, for these rules, a torch you're holding and the sun are the same thing, within the "bright light" range of the torch (20'). Outside of that range, the torch stops providing bright light. Get some distance on someone with a torch and you move into shadowy illumination against them instead. (If you have different vision modes than they do, you could actually have different conditions to see them then they have to see you, depending on the light.)
example:
If you're holding the torch, you're in bright light and can't Hide without Cover.
If someone else is holding the torch and you're 5' away from them, you're in bright light and can't Hide without Cover.
If someone else is holding the torch and you're 25' away from them, you're in shadowy illumination. That grants you Concealment, and you can Hide.
The same rules apply for any light source, you can use the Vision and Light table for the effective ranges of different light sources.
So what's Sunlight do?
The sun creates both bright light and bright sunlight. The difference is only in the case of monsters or effects that mention something related to that, like an Orc:
Orcs are dazzled in bright sunlight or within the radius of a daylight
spell.
A torch doesn't generate bright sunlight, so in this case it's different.
This Creates Lots of DM Interpretation
As you noticed, this gets confusing pretty fast when Shadowdancers get involved. Just what is "some sort of shadow", and where is it? Ask your DM. It's relative to the light, the position of the light source, the size of the thing casting the shadow, and the rules don't have anything to say on the matter whatsoever.
How big a shadow do you need to use it? Doesn't say. How much shadow is enough shadow to shadow jump? Doesn't say. How long is the shadow being cast by the enemy in front of me? Doesn't say. (This is probably why Pathfinder changed the wording on some of these abilities to be near "dim light" instead, which is more of a known rules thing than "some kind of shadow.")
As a DM dealing with a player who uses these abilities, it can get pretty confusing to try and sort out. It's actually easier in a dungeon with no light of its own, because if some player is carrying a light source, we can map it out on the board pretty easily relative to them and see where the shadowed areas would be (and which direction the player shadows are going, if you want to hide in the shadow of the Wild Shaped Druid).
But in an outside area at 5pm? Where are the shadows in that? It's a lot of work to sort out exactly how it all works, and it's often easier to come up with a simple rule of thumb and apply that rule of thumb consistently.
Hide
The one exception you mentioned is "how dim is dim enough?" In order to use Hide, you need concealment. Shadowy Illumination provides that. So you need to be in Shadowy Illumination, which is going to depend on what the area's light sources are (but most of those have a radius of providing light, and the table in the first link I provided has those distances).
You also need to be not being observed. If they're watching you, even with Shadowy Illumination, you can't use Hide. "Watching you" basically means they can see you at all, because in D&D vision is omnidirectional: characters are looking in every direction on every turn.
That's part of what makes Hide in Plain Sight so good (with HiPS, you can use Hide while being observed).
Low-light vision lets you see color!
Within the 120' radius of a deep gnome's darkvision, he only sees in black and white without the presence of a light source. Within the radius of a light source, folks can see in color whether it's inside their darkvision range (if any) or not. Low-light vision doubles the radius of illumination from all light sources, thus doubling the range the deep gnome can see color around a light source. This is useful.
Low-light vision has great advantages in distance!
Low-light vision's range is not fixed, nor is it centered on the gnome: it simply doubles the radius of a light source, no matter where the light source is or what its radius. This lets the gnome see things which would be hidden to creatures with only darkvision. For example:
If a torch sconce (20' radius of bright illumination, but 40' for the gnome) is 200' away from the party, then a thief sitting 30' away from the torch can make Hide checks to avoid detection by both party members with normal vision and ones with 120' darkvision. However, that Hide check automatically fails against the gnome, for whom the thief does not have the benefit of shadowy illumination to hide in.
Best Answer
The extraordinary ability low-light vision is a mess...
The elf racial trait low-light vision says
The Player's Handbook on Vision and Light adds that one should
The Monster Manual provides a similar description of low-light vision that's slightly more explicit:
And the Dungeon Master's Guide provides a description of low-light vision:
Finally, the Rules Compendium provides another description of low-light vision:
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...
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
So the DM determines the distance randomly. Then according to the skill Spot
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.