Thorpe has quite a neat lineup of thrilling flats, but let's not forget that the newest one of those (Rush) celebrates its fifteenth birthday this season. Save for the two small flats in Old Town and the Dodgems on the midway, all of Thorpe's flat rides were built before 2005. For the record, they've built three coasters and refurbished another since then, so if they're due anything, coasters don't seem to be it.
Don't get me wrong - if Thorpe were to get a new flat ride I wouldn't complain. But I don't think the GP know or care enough about how old the current line-up of flat rides are to warrant investment in a new flat when the park has the best line-up of flat rides in the UK and probably one of the best in Europe, thinking about it. The fact they have a bunch of flats is good enough in comparison to some places *cough* Towers.
The thing the GP are more likely to recall is that there hasn't been a new coaster in a while. Even I, as an enthusiast, regularly forget that the Walking Dead ride exists because it's very uneventful. The Swarm is surprisingly like 8 years old. I'd definitely say Thorpe are due a new coaster soonish, the last major ride investment is also 4 years old this year and that isn't a coaster so I think many were let down by that. I think they are definitely approaching new coaster territory now.
The difference with AT is that they've steadily removed all of the major flat rides. Towers have seen 2 additional coasters since The Swarm debuted, which is good. But they need some decent filler attractions to pad out the crowd levels and to justify a visit (in my opinion). I've not been interested in the place for a few years now, mainly because it feels like there's no depth to the Towers experience anymore. It's just a few coasters which are unreliable at the best of times, and then not much else. Then you go somewhere like Europa Park, which on paper should be of a similar caliber, but in reality it's just leagues ahead in terms of the experience on offer.
As much as I like coasters, I don't think that quantity beats quality. Sure you could probably get a coaster for the cost of a big flat ride, but I don't necessarily think that's going to be the best option in the long run. A decent flat ride with the right marketing is still going to work. I'm sure Merlin could market a cardboard box if they had to!