Honeslty when thinking about the next major investment, like towers the park doesn't need "just another coaster" The coaster line up is probably pretty stable and more than enough veriaty and capacity. What the park is lacking is secondary experiences that the crowd who ride the coasters want to do. Looking at the parks history, the last brand new thrill flat investment was Slammer and Rush in 2005. You had Storm Surge in 2010 which was a relocated ride, the dodgems in 2014 which straddles the line of a thrill flat. and of course Ghost Train in 2016 but due to the complexity in maintenance and staffing I would class this more like a coaster in its operation than a thrill flat. But even if you did thats almost 10 years since the last proper flat ride (mainly due to habit of making walk through 'Merlin midway' mazes as attractions) What the park needs is a thrill flat package similar to how Zodiac, Vortex and Detonator where done, and more recently the Rumour that Toxicator at Towers was bought in a multi ride package. With the right ride choices this would work as a solid coaster level investment with the benefit of also being able to spread out queues around the park.