Dreamscapes, dream magic and such are very creative realms that are highly dependent on player & GM creativity and cooperation.
dream on AoN. The other source to reference is Occult Adventures.
Dream Travel:C[TP][Mndafct]6, besides being of the teleport type, the spell near the end says, "Traveling to a different planar destination decreases the accuracy of your dream transit. If you exit a creature’s dream onto a plane different from the plane you started on, you end up in a random location on the destination plane." which means you and the spell targets travel physically. Generally the Plane on which you cast a spell does not matter (there are exceptions as listed in the spell description and/or the Planar Traits of said Plane).
Are you asking what happens when you cast the dream travel spell while already physically in the Dimension of Dreams, or what happens if you're just visiting in a lucid body (not your physical body) and you cast the dream travel spell, either because that's part of your normal spells or because you're using an impossible dream power to cast the spell you don't normally have?
If you're physically there, dream travel can't physically pull your body into the dream realm from the Material Plane (or at least, any other plane), I'd say it probably doesn't work.
Now, a GM might be inclined to have it start guiding you to a chosen creature's dreamscape (if they're sleeping). I don't think that would cause any real problems in most cases, but I don't agree with it because at that point you've got things within or occurring in the Dimension of Dreams affecting or targeting things in reality (that aren't listed as exceptions). Like casting charm on a dream version of someone in a dreamscape and somehow in reality they get charmed by you (whether that was really their lucid body because they were asleep and their monadic soul was there, or because it's just a figment of the dimension).
If you're in a lucid body in the Dimension of Dreams, casting it probably wouldn't work any different. It wouldn't affect your real body and pull you in because that seems inherently against all the intents of the Dimension of Dreams other than the exceptions listed. Even if you cast a carefully and specifically worded wish I don't believe you can affect anything in reality or outside of the Dimension. Even if you gave yourself a permanent inherent ability increase, it probably would only last while you're there. I wouldn't even have it carry over into future visits.
You don't even get experience for what happens in there (unless you're actually physically there), though you might remember the experiences or use them to aid a decision later (such as not trusting a new advisor because you were betrayed in a dream, whether he really is going to betray you or not, or whether he really is a reptilian in disguise).
Casting dream travel while 'visiting' might take your lucid body to the dreamscape you want, but I don't see how it would be ultimately any different from just ending up there any other way. You wouldn't be able to actually pop out on the creature's home plane and have your physical body be there. If it did happen, it would likely just be a dreamscape scenario of it, created by your influences and desires by the Dimension of Dreams. In other words, you'd just be affecting the reality of the highly morphic dimension, but not actual reality.
Let's say you're in a lucid body in a dream (not physically there such as during dream travel. You don't have your friend Jim anywhere in sight. You cast dream travel from in the dreamscape to locate Jim's dreamscape. Now, theoretically, there could be a dream Jim. Does your dream dream travel target real Jim based on if he's sleeping or not. Or some quantum Jim incarnation that might exist within the current dreamscape you're in (because there's no reason you can't walk into a dreamscape that has Jim's house and encounter a Jim, who might even be asleep in there)?
So, ala Inception, if during that time, dream Jim wakes up, are you kicked fully out of the Dream Dimension, or just back to the actual Dream Dimension? Most likely you'd still be in the Dream Dimension.
The existence of real Jim and his wakened or sleeping state probably doesn't matter in this case (since he isn't the reason you're in the Dream Dimension in this case), but if you saw a sleeping creature in the dreamscape, they'd technically be a valid target for your dreamscape casting of dream travel. In that case, even if that exact identical creature existed in reality, whatever its waking or sleeping state would have no bearing on the outcome of your dreaming dream travel spell, only the dreamscape target.
Similarly, if you were in a dreamscape and cast scrying I don't think you'd really see the actual reality vision of what's happening, only a vision of what a dreamscape version of the target might be doing in that particular dreamscape or a dream's realm figment. It would be like calling someone on the phone in your dream, and expecting their phone in reality to ring. A cool concept and a great story, but I don't think that's how it works in the situation you're asking.
I don't believe that any creature should be effected or even targetable in reality from within or by a dreamscape spell or power (unless it specifically says it can do that).