This is a good one as I'm sure there's so much that everyone would like to see!
For me I would like to see in the future if I had an unlimited budget/ anything goes.
1. Add a couple of decent restaurants to the main entrance and increase opening hours to later in the evening. Maybe add a fireworks from the towers nights at weekends with projections.
2. Removal of Spinball to another location in the park (maybe re-themed into the dark forest somehow inside the woodlands) to extend ceebeebies land into a larger area for families/kids.
3. Addition of a new water ride into mutiny bay and move the blade into this area somehow.
4. Change of Duel to a "haunted mansion" style ride like Disney with a constant capacity - so nice short ques! And addition of something else into gloomy wood - ghost themed.
5. In the area where the blade is removed addition of a maelstrom style ride with a huge cog on the end.
6. Galactic back to air with waterfalls and full theme given - like it should have been.
7. Dark forest never realised its full potential for me so removal/change of Rita to the broomstick ride- with a theme of witches of the forest/ wraiths from thirteen, or Escape from the woods-mans lodge where the carriage could be a huge fallen tree trunk which has a back story (could be linked to hex) and lots of near misses to huge axes as you ride the tree trunk through the woods!
8. Enterprise given a facelift and brought into the style of the smiler to fit in with the area - maybe a huge spinning spiral on the main central part would look good when it's spinning around.
9. Regeneration of the towers with a dungeon ride - entering the lost dungeons of the towers (maybe a scare maze idea?) or even an exclusive small amount of rooms which could be a hotel for the night?
10. Main lake addition of a bar/ restaurant with a fountain show in the centre of the lake (maybe even something like fantasmic at Disney) with projections for evening entertainment I think more things at night would make the hotels even more popular.
Obviously these are all imagining an unlimited budget but I would love to see something along these lines at Alton Towers. I'm sure whatever they have in the pipeline for the future is going to be great!