Well, here is my take.

Since I started with Poser V3 has always been my character of choice to work with....mainly because at first everyone was "v3" this and that due to the fact that there really weren't a whole lot of choices other than the poser figures and the Daz ones.  In time I expanded to also include Aiko as one of my favourites because I started to see more character packages that were getting away from that Anime look which I'm not a huge fan of (though now it's grown on me and I find some of them cute).

When V4 first came out I wasn't one to jump on the bandwagon because I'm not one that has to have the newest toy as  soon as they come out.

I did eventually end up buying V4 mainly because I saw a few character packages that were cute and some cute looking clothing for her that thanks to Wardrobe Wizard I can use on V3 and Aiko, but I needed to have the figure in my library to do so.

TBH I don't really care for V4 all that much.  Her eyes look weird to me and I can't get used to the way she functions in the parameter dials.  Plus it seems that so many characters being sold for her look so much like each other, and the skin textures look plastic. Now that is no fault of the figure itself, but a figure is only as good as the products available to support it.

These days the only time she is usually loaded into my Poser is when I want to convert some of her clothing to another figure, or when I'm beta testing stuff for her. Other than that my figures of choice are still V3 and Aiko.

One thing that I do like about the V4 figure though is the fact that sometimes the clothing is made so that it accepts the V4 character morphs, so all you have to do is INJ the character into the figure and then into the clothing and the clothing automatically fits, even when posed. However that isn't a feature with all of V4 clothing, just some.

There are way more freebies available for V3 than there is for V4, both in clothing, props, and character morphs/textures.  So if you are looking for value for your money, then stick with V3.

If you are one that needs every new toy on the block, then go ahead and buy V4 and then decide for yourself if she is "worth" it, because basically it really depends on what you are looking for in a figure.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi