1. Yes, the market is moving. Quite steadily to Genesis 3 and in turn Daz Studio. There really is quite overwhelming evidence to demonstrate the fact from multiple sources. Here are some things to consider: Site traffic, New Product release volumes, What's Hot sections and Vendor support. Vendors in fairly substantial numbers are moving to Genesis 3 support, here are just a few you may remember. Ironman13, Dreamlight, Sabby, 3DSublimeproductions, Pretty3D, Kaleya, Powerage, Outoftouch, Exnem, Godin, designem, Silver, Sveva, lilflame the list goes on and on. Genesis 3 is currently the figure with the most wide spread and up to date support, from the broadest selection of vendors.

Is it "Artist Preference"? well yes and no. Most vendors will prefer to support the market leader due to viability of return on their investment in the creation of products. Making freebies for a niche market is an entirely different scenario though. Generally products become the market leader for a number of reasons, including increased capability and support and not least market appeal. I would say Artistic Preference is more an influence on those preferring to continue to create for V4 despite market indicators.

There are a wide range of add on products available that will keep your current content library viable if you do want to experiment with Genesis 3 and DS. There are only a few things that don't make the leap across, like figure material skins. Though it's worth noting that most are not configured for modern PBR renderers anyway (Iray or Superfly) and would need work in any recent app to look decent, including Poser 11.

More info about Genesis 3 is available here if you are interested: http://www.daz3d.com/genesis-3

2. .duf is not an "older file type" it's the current file type for use with Daz Studio assets, it is generally a compressed file and has many applications within DS. More info about Daz Studio here: https://www.daz3d.com/daz_studio

3. Well like anything it's only a waste if you have no use for it. Different tools will help give you a broader range to your capabilities and expand your creative tool set. May I add that Daz Studio (Full version) and Genesis 3 Bases (Male and Female) are both free so there is no reason, if you're interested, that you cannot download and make your own assessment on which tools you prefer or suit your task better. Or even more mind blowing, use both Poser and Daz Studio for what they each do better! But if you do prefer a Birmingham Screwdriver for every task, that's also your prerogative. :)

The most important point is. To me there is no reason to "move" at all, just because you install Genesis it doesn't mean you need to delete V4. Or if you install DS that you need to uninstall Poser. You can have the best of both worlds and use each and every tool to help you create, without discounting anything due to some imaginary tribal division.

So Good luck, I hope you find what works best for you. But don't be afraid to try something new once in awhile. It can be quite refreshing and inspiring. And don't feel the need to restrict yourself to fit someone else's ideal of what is right for you. Only you can truly judge that.