Using the Pink Lodge would be a great move if you ask me, but I can imagine the practicality and setup required would be too much to justify it when they already have hotel rooms with all the amenities and utilities needed.
If you think about it, you'd need to take staff out of the hotels to supervise everyone in the lodge, which would inevitably mean having to pay extra staff at one end or the other. You need to get all the beds and facilities into the lodge. You need to make sure you've got proper facilities for the guests. It's no use them having to walk through the gardens to find the nearest toilet
You would also need some way of escorting the whole group to and from the restaurants at the hotel for dinner and breakfast to ensure they aren't all wandering around the theme park late at night or early in the morning. As awesome as it'd be to do something like this I think there would just be too many complications in making the idea work for them to consider it
That said, it would be awesome for them to turn one of the larger buildings, like the Pink Lodge into a scaremaze/zone for Scarefest. Make it a walkthrough attraction where groups can pass through, going from room to room and watching different scenes!
I would actually be quite surprised if they don't use the Pink Lodge for storage actually! If there isn't anything in there I'd be very surprised! If I remember rightly, the Swiss Cotage has a few things in it back from its days as a staff traning room, and a green room(?). Apparently, it even has network ports in a lot of the rooms from when it as used!
If Alton are blessed with one thing though, it's all the buildings they have dotted around the site which they can use for storage. It completely eliminates the need to build a big, ugly, tin warehouse in the park