Do I Need a Mirrorless Camera?

The mirrorless market and its Nikon CX mount came pretty much out of nowhere a few years ago, and it keeps going strong. There are all kinds of speculations about the future of photographic formats - one rumor I've read somewhere is that Nikon will eventually want to have only two formats, DX and FX, with DX sensors found only in small mirrorless bodies, and FX sensors for its higher end models. In my opinion, this isn't anything in the near future, but clearly, it will not be difficult to imagine. Simply stop producing DX SLR cameras, start producing DX mirrorless compacts, and then voila! You have a series of mirrorless compacts that can take DX lenses.

The smaller sensors of mirrorless cameras (here a m4/3 Olympus) don't handle noise as well as the bigger sensors found in DSLRs. But they can still hold their own

But do you need a mirrorless camera? Well, only you can answer that, but here are a few things to consider:

+ significantly smaller/lighter compared to DSLRs. Not only the cameras, but also the lenses are smaller.
+ new technology, continuoulsy updated and upgraded.
+ currently, their smaller-than-DX sensor means they can take (with adapters) a vast range of lenses from other mounts

- not pro-level, at least for some kinds of works
- the sensors, as long as they are smaller than DX, will always be somewhat inferior to their contemporary DX counterparts (not to mention FX)
- For full compatibility (i.e. autofocus, VR), the lens options are more limiting compared to DX/FX

So, what is a mirrorless camera good for? Which is the intended audience? Well, as you can probably conclude yourself based on the observations above, the ideal mirrorless camera user is an amateur/intermediate photographer who travels a lot, often to remote and difficult to access locations. If you're climbing the mountains of Nepal, enjoying the glaciers of Iceland, or are in a photographic safari in Africa, a mirrorless is a really attractive solution.

Bonus +:
+ smaller sensor also means higher crop factor. In other words, if you attach your Nikkor 300mm f/4 to your Nikon J1 mirrorless, the crop factor of 2.7 (compared to 1.5 of DX) means you have a lens that is 810mm in full frame terms! Now, that safari in Africa starts to sound interesting with a mirrorless, doesn't it?

(of course there is the oxymoron of attaching a gigantic lens to a tiny camera, designed for compactness. But the point is, you have the option to do so if you want. If you don't need that much reach, just go with the CX format lens, which is small and compact)

On the other hand, mirrorless technology has not yet reached the stage that it can render the big fat pro DSLRs obsolete - nowhere near. The reasons are mostly related to speed/performance and sensor image quality. As mentioned before, as long as the mirrorless sensor in the Nikons is (generously) cropped, it will inevitably lag behind the larger sensors, particularly in high ISOs.

When you're in the middle of the forest in -20 degrees, traveling light can be a huge benefit.

In conclusion, like with all other purchasing decisions, the only person who can answer the question "Do I need a mirrorless camera?" or "should I get a mirrorless camera?" is you. Investing in the CX format is not as big a decision as e.g. choosing whether to invest in Nikon or Canon. Even the DX vs FX is comparatively more difficult. The reasons are:
a) The CX format is relatively cheap(er). Cheap lenses, and quite cheap cameras (particularly if you don't "need" the latest and greatest). An investment of $400-$500 is not a big deal, compared to $1000+ for a DSLR and couple of lenses or  $2000+ for an FX and a single lens.
b) Occasionally with some limitations, it's easy to use your existing Nikon lenses with a mirrorless camera. So, ultimately, you don't need to invest in a wholly other system. You can easily try mirrorless, and if you don't like it, no big deal: you sell the camera and you continue using your DX (or FX) lenses with a DSLR