I have gone Solo my last 2 trips to the World, and I enjoyed every minute of it.
Some tips -
1) As a poster above me stated, try and do something new each time you go. The first time I went solo, I did ToT 5 times in a row, and when I came back, it was still fun, but not as exciting as the first day I rode it - so the last time I went I did RnRC.....probably about 8 times! If you have done all of the rides, check out a show for the first time - Flights of Wonder was a lot more fun than I thought it might be at AK, and Indian Jones at DHS wasn't as great as I hoped, but it still had that novelty "new" feeling to it.
2) I usually don't eat at the Full Service restaurants, but this trip I am going to do that Solo as well. The only downside (I think) will be at Crystal Palace and trying to get a great picture with the characters ----- but many people have told me to either ask a character attendant if they are there, or just ask a family next to you, and then take theirs!
3) If you like music (I play piano and do vocal direction for theater) then check out the Ragtime pianist by Casey's Corner, the Dapper Dans on Main Street, or enjoy the Trolley when it comes by with the Cast Members! Most times you can get rushed right through these things, so if you think you will like it, check it out.
4) I learned on the last day of my last trip - if I see a cast member at a kiosk selling something, then I just take 5 minutes, and strike up a conversation - and I ask them what is one thing in the park that they would love to do today - then I go and check it out, even if it something I don't think I would be that interested in! That's how I found about Birds of Flight and it was great!
5) Have an amazing time!