I believe that the park have got the budget to sort out the themed feature that housed the fireball.
Of course, it's very unlikely that the fireball special effect itself will return. The gas lines had to be cut during Stealth's construction and to reroute them would be incredibly difficult.
But the actual ball feature (whatever the name of it is) should make a reappearance.
It's certainly fair to say they've done small improvements here and there. On a more blunt point, I think it's also fair to say that many of these have been done because they've needed to be done (ie: because Merlin's H&S deemed it necessary).
Equally, there's been small changes with branding, some refreshed food and retails outlets and so forth. In my opinion these are things that most parks should look to do regularly, but it's sadly the case that Thorpe didn't always do that in the past. So it is good to see it's been a common theme in recent years.