Phane sucks, I agree with you 100% it would probably still suck even if it had 40 lines instead of 4. Succubus on the other hand is awesome and will not be a Yrthak of any edition.
The thing is that the time spent giving the phane something to do in the first place could be spent giving the succubus something FRESH to do.
Anyone who's vaguely familiar with fantasy tropes will be able to connect the dots for a succubus-tempting-the-king kind of plot. It's archetypal to the point of cliche. The succubus MM entry can nod at that in one sentence, and spend the rest of the entry describing one possible twist on the scenario (perhaps she's an intellectual succubus who is completely chaste but who warps people's minds by having their darkest desires embodied -- she doesn't promise them pleasures of the flesh, but pleasures of the mind!).
And in the space that they describe that, when it comes to the phane, they describe how it travels back in time to kill the PC's as babies (or whatever).
I do have enough confidence in the designers that they can give some pretty good coolness to any monster that they BOTHER to give coolness to. And in the case of monsters, I'm perfectly happy with ONLY the ones they give coolness to.
And this includes (but isn't limited to) out of combat coolness.
It's kind of a shame that we haven't seen or the phane didn't get any plot-love, because it doesn't HAVE to be the ythrak of 4e, and D&D can absolutely go beyond the mythic creatures with pre-packaged archetypal plots (the githzerai/githyanki/mindflayer triumvirate is pretty good, even the Shadar-kai aren't too bad in that respect).
But if what we saw is what we'll get on the phane, then that page is a bigger waste of space now than it ever could be if it were replaced with a goblin lair.
Reprinting those and the extrapolation ideas with every humanoid monster would be even more insane.
But something like: "The phanes know a ritual that allows them to travel exactly 20 years back in time. (print the four lines of the ritual) They often find themselves searching for treasure through lackeys and minions (such as creature X) to finance these rituals, in order to take out prominent champions of both good and evil gods retroactively, when they were children."
That's a solid adventure in 10 lines -- I have allied creatures, I have a motive, I have a target (some NPC cleric or paladin perhaps), I may even have a twist (the PC's have to save an evil priest from the phane in order to assure that the good he did while younger still remains in effect), or whatever. I even have a reward, of sorts -- if the PC's discover the ritual, they can go back in time and fix something that happened 20 years ago (which may itself lead to more adventures!).
It doesn't need to be exhaustively extensive, any more than every sword wound is exhaustively extensive, but there needs to be something, because, as always, Make Stuff Up sucks as a rule.
DMing is a hobby, it requires some spare time. Even with maximum external support.
This is kind of a bigger question, but I think that 4e wants to make it take as little spare time as possible, and if it can eliminate it all together, it will be a good thing.
As it is I can run 3e without any preparation time. If I just use the core books, it means fighting a lot of monsters and not a lot of NPC's, and ignoring the "filler" like the phantom fungus, but I can absolutely do it. That's the way I prefer to run games, and part of the reason I can do that is because, for instance, blink dogs and displacer beasts have an inherent rivalry written into the fluff in a single sentence, or because bodaks still retain some of their memories of their past lives, or whatever.
But if 4e removes that fluff (as it has apparently done for the bodak), it'll suck just that little bit more for those people who COULD run the critter fresh out of the box, but are left going "Meh. Sounds dumb." Just because it lacked a few key sentences about motives and, perhaps, a few key mechanics for how it does what it does when it's not beating up PC's.