Thomas Land did not increase investment at the park, it halted it almost. Before Thomas Land we had large attractions such as G-force, Excalibur, Maelstrom in the years preceding. After Thomas Land we had almost the entire back catalogue of small and cheap Zamperla rides being added. With the exception of Ben 10, but even that was pretty small by Draytons standards.
I can see why they did that though, as they were loosing visitors massively towards 2006. Thomas Land brought visitor numbers back up, but after the initial investment of the area, investment levels up until this year, have been a shadow of what they were pre Thomas Land. Remeber Excalibur too, that was a same investment level ride as G-Force, lasted even shorter than that.
The park was great in the 90's and early 200's though. Really good place with a massive variety of rides and highly themed rides.
On another note. Could it not be argued that Paultons decided to become the Drayton of the south? While their new investments are fantastic and have outshone anything Drayton have done in a long time. From what I can see, Drayton has always seemed to have the better ride stock and themed attractions. Obviously that is changing now, but it seems to me it is Paultons who have tried to emulate Drayton over the past decade or so. I have not directly been to Paultons so there may be something I am missing. Either way, it is great, great for the UK industry.