Originally Posted by
Cage
What would I do if I was in your position?
At this point I'd keep the D5500. It has the highly regarded Sony sensor, and with the right lens will produce images that will delight and astound you. What it won't do is auto focus with non AF-S lens.
I'd go for the G1 Tamron 70-200 f2.8 VC (I had one and it was excellent) and also replace your 17-50 f2.8. On the D5500 that will give you the FF equivalent of 25-75mm and 105-300mm, if you want longer you could add a 1.4 T/C.
If you want to try UWA shots, the very good Sigma 10-20mm would be a good starting point.
I'd also consider buying the Tamron from a reputable Grey Market seller as they don't seem to have any inherent problems, the lens that is.
Just my two bobs worth.