A few years ago, the main reason to buy and use DSLR where mainly the following:
Better images quality
Optical view finder
Great control of the depth of field (thanks to bigger sensor and faster lenses)
Better controls and ergonomics
Faster AF and many images per second
Access to a full photographic system of lenses, flashes and other accessories
Nowadays, thanks to enhanced sensors, mirrorless cameras, miniaturization, specialized cameras for every kind of photographers, most of these reasons have become less and less true. Of course it still makes sense for some professional photographers, of course I and many amateurs still prefer shooting with a DSLR but as a matter of fact, I like to say the main reason to still go for such a camera is: “I don’t want to compromise”. “I accept to pay a lot, to carry a heavy bunch of gear, to have several bodies and many lenses and accessories, because I will also accept to spend hours on post processes of my images. All I want is the best gear available to let me have the pictures like I want to”.
This means an APS-C sized sensor (DX for Nikon) DSLR does not make sense any longer but for those who never tried beforeap one (like a Nikon D3200 which costs less, by far, than a mirrorless whereas able to make really excellent images). Frankly – I own a Nikon D7000, I don’t see the point having nowadays a DX DSLR when you are an “experienced” photographer. Full frame (FX for Nikon) cameras are becoming really affordable and are somewhere, the only consistent option for a DSLR given the present competition of great mirrorless cameras and excellent compact cameras. Back to before 2000, at this time, only such cameras existed!
It does not mean the manufacturers will stop developing lenses for DX, nor will stop releasing new cameras (Nikon refreshed its D7000 recently by the D7100), I just don’t recommend investing into a DX DSLR system. If you have one – like me – you can still use it a secondary system, or because it still works very well but the DX time, basically, sounds to be over to me. Buy FX DSLR cameras if you want no compromise, and middle format should you be able to afford it. Again, if you are on budget, a DX DSLR could be your first DSLR, but it will just be “temporary”. And don’t forget mirrorless, compacts and smartphone as complementary but “mandatory” cameras.
Nowadays, it does not really make sense to own just one camera. And certainly not a DX DSLR!