I know this is controversial. But I think a non-wristband theme park is always going to struggle to maintain the ruins of a gothic country house, as an attraction in itself.
Access means upkeep. The more free the access the more it needs to be monitored, kept safe, the more damage the little that is left will endure. As a fully open free-roam attraction, for a safety focused, good-custodian theme park operator, it could end up being the most dangerous and most maintenance hungry attraction in the entire resort. For what improvement to their theme park offering? And if that improvement is only slight, marginal, how is this shift to open access being paid for?
Now personally, I love the Towers, it's a gorgeous house to me, even gutted and rotting. But any attraction at a theme park needs to pay it's way, either in marketability, increased guest satisfaction, or directly creating revenue.
"We have a relatively mid historical attraction, a stones throw from Little Moreton Hall, Chatsworth House, Shugborough Hall, Trentham Gardens, Biddulph Grange, Calke Abbey....come see our inferior ruin and gardens for £29-68pp! When you get here, please excuse the fact that it's literally falling apart, don't think too much about how insensitive most restoration and efforts to secure the ruin have been, try not to feel too uncomfortable about the unattended school group vaping on the spiral staircase, and don't be alarmed by the loud screaming echoing through the unglazed windows at regular intervals"
It just isn't right for the resort at this moment in time.
And here's where I probably get really controversial. The best thing that happened to Alton Towers itself since perhaps the 20s, is Hex. No comparable ruin in the area attracts such footfall through it's doors. Very few decaying country houses can entertain such a wide range of guests with a slice of local history. The safest, most structurally sound part of the entire building, is now the Armoury and the Octagon.
The Towers as a part of a theme park are managing, as they of course did for nearly a hundred years as a standing home, and for a few decades as a stately ruin, to wow and excite a new generation of visitors. The majority of the still standing building. was originally built with a spirit not too different to that of Oblivion's hole, or Nemesis' station, or Curses façade. Alton Towers House and Grounds, as we see it today was always a theme park. Keeping to that spirit, and utilising the shell to continue entertaining visitors, I think is a great way forward.
I think Alton Towers should sensitively use most of the structure for sympathetic, interesting and unique theme park attractions. Being a major theme park shouldn't be an inconvenience to the life of the ruins and grounds - they should use their skills, experience and funding as a way to make them relevant, safe and there for future generations to enjoy. After all, that's their responsibility as a heritage custodian.
Fill it with Hexes.