To me the biggest difference is that the D5200 has auto bracketing and the flip screen. Auto bracketing creates multiple exposures without the manual fuss.
There is currently quite a price difference between the D3200 and the D5200 due to the D5200 not having any promotions since it is so new. I called the camera store where I got my D3200 yesterday and they said when they get the D5200 in, I should come in and see if I like it better. If so, they would see what they could do for me.
The more I look at the flip screen and evaluate the auto bracketing feature, I'm not sure it would be worth the price difference. I only see using the bracketing for HDR photos and I'm not so sure that is that important to me. Are they any other uses for the auto bracketing that I'm not aware of? I'm not really fond of the flip screen either.
Also, I think the processor might be slightly improved on the D5200, but I'm not sure it would make that much difference. I'm happy with the D3200, but I don't want to feel I got gipped because I didn't know what I didn't know at the time. I was looking for a step up from my D60 and something that I could grow with.
Any input would be appreciated!