So what if a few enthusiasts travel for a coaster? That won't fix the park's other faults.
Walibi added theirs on the back of a long term plan of changes (whilst the owners are seemingly heavily involved in given the additions to the other parks in their group). But when you go to Walibi the park isn't in a complete state of disrepair, adding crap small additions that cost all the budget to run. The food doesn't cost the earth, the operations aren't terrible (nor are they good), and they certainly didn't invest millions into the "future of theme parks" to see it fail.
What's missing from all Merlin parks is a viable long term plan. Though Chessie and Towers have suffered less as they sort of have one, Thorpe has chopped and changed almost yearly. Redo NWO to become family friendly, change it to adult orientated theme. Add family theme area to park in attempt to get them to visit, then give up after a year.
The first thing the park needs to do is improve the infrastructure in preparation for the next big thing. Through sensible small additions building up to whatever massive coaster they build. But that'll only happen if Merlin have not only a plan for the park but to invest correctly and not focus on crap USPs that don't help the park progress.