I have traveled solo in the past: New York City, DC, and Cape Cod.
I enjoyed New York and DC very much. As cities, they offered a lot and the solo vacationer hardly gets much attention, likely because so many business people also travel solo. Cape Cod, while relaxing, has much less to do than any city, and since most do not travel alone you do stick out somewhat. Granted, compared to some places, I feel as though it could have been much worse, but I would probably only go back to Cape Cod not-solo in the future.
That said, any suggestions for a future trip? I have very loose plans to take a trip in early February, but right now I do not know where to go. I'd like to stay in the States, preferably somewhere warmer than the Northeast. That said, I need somewhere that won't break the bank. I looked at the cost of hotels in Key West and they average $400/night around that time!
If you have seen me on other threads, I am knee deep in planning a large family vacation for Fall 2016. This trip, in February, will be just me.