Sorry if I disagree, but displacement is for gaming.

Firefly as it is implemented in Poser is a dud and I avoid it whenever I can.
Even in full production mode the Poser 4 renderer will easily deliver a sharper, more crisp render.
And I'd absolutely hate having to work with a nondistinct blob in my preview window which only transforms into a human being AFTER it is rendered. It irritates me to no end.
Same when the lights look completely different in the finished render than they look in the preview.

We can agree that Miki, Miki 2, Jessi, James and the G2 series are WAY overweight. That's why I made my own LoRez versions of MIKI and Sydney.
I also often use M3RR or V3RR instead of  standard V3 and M3. V2LO and M2LO are also very fine figures.

But a realistic mesh needs bodydetail. Actually sculpted muscles, knees, shoulders, ribs and enough polygons in the face to render smoothly even without artifcial polygon smoothing.

So for clothed figures I use M3RR and V3RR.
For unclothed I use a combination of Unimesh body (Laura, V3, SP3) with a V3RR head.
For characters that need full head detail like wrinkles and folds (Old people, creatures), I use full rez M3 and V3.

Sorry, but Posette and Dork just don't cut it for front row use any more.
Their bodys are fine (Especially Dorks where the mesh nicely flows around each muscle group), but they both need proper kneecaps and a few more polygons in their faces especially around their eyes.
You can do what you want with Posette and Dork, but their funky blocky eyes and mouths will always give them away unless that problem is solved.

As I said, I'm all for light, efficient meshes, but faking  bodydetail with a displacement map is not the way to go for Poser still renders.
It's good for gaming and maybe to add detail to inanimate background objects, but the human body should be properly modelled with all the necessary detail.
Not only because a displacement map can not properly interact with different lights, but because as an artist I am just not inspired by an undetailed bag of polygons.
I must suspense disbelief, and I can only do that if a mesh I'm looking at in the preview window has all the proper features of a human being.
Same reason why I never use "box" or "fast" tracking.

Otherwise I could just use woody with a killer displacement map and be done with it.

V3 and M3 and all the other Unimesh are a product of the time when DAZ did only support P4, so polygon wise they are a bit on the high side.
But due to their injection technology they work fine on the majority of todays computers.
Abandoning injection technology was the most asinine thing DAZ could have done.
The problem never was injection itself but the way DAZ implemented it with a gazillion of folders and readscripts, and those vocal users who couldn't be bothered to read a manual.

V4 looses any eficiency she might have gained over V3 with her (slightly) lower mesh weight due to the fact that she permanently has to carry 69 magnets and all her morphs around in her cr2.

To make this possible, DAZ HAD to reduce the absolute numbers of morphs.
So to all you people wailng and gnashing your teeth that DAZ didn't include your favorite V3 body or headmorph:
It's not that DAZ wants to make you to pay extra for them (Ok, maybe they do. Lol), it's just that 99% of todays computers simply can't handle a V4 sized mesh with all possible morphs permanently present.
You can thank all of the "Injection is crap" folks for it.

Morph injection IS the only way to give meshes above the size of 20.000 polygons a reasonable amount of morphs without your computer slowing down to a crawl.

Back to the original point:
DAZ meshes are popular because the are GOOD.
Plain and simple.

Not that DAZ meshes can't stand improvements.
There is a LOT wrong with V3, and after a lot of attempts I completely gave up hope to turn V4 into a reasonable representation of a human being.

But they are still better than the rest.