Every single DSLR bodies of the last generation (except D7000 & D300s) were replaced this year, with the introduction of D600 as an enthusiast FX camera slots right in between D800 & D7000 (or D300s), Nikon is like having a camera diahorrea.
Actually, it is probably the genre you are in. From your flickr, you are more into portraits I see. But for people like birders, wildlife, as well as sports, having remote control can be a godsend. This is apart from the usual wedding/event photographers.
I think too, D5200 does not have built in motor, so lesser choice of lens. Lens like 50mm 1.8D can produce great images, and cheaper, and other AF lenses are superb .Other choices are Tokina 100mm f2.8, Tamron 18-200mm, etc.
even though D5200 has a better specs (esp. megapixels), u r upgrading from an entry level to another almost entry level dslr...ikt's quite pointless i tink. i won't upgrade if i were u, better wait for the D7000 or D300s replacement (if there is).