It would take a bit of work, but It's probably possible to write a code to update the Addventure, while still keeping the old episodes. The only problem I see with it is that the format of the old epsidoes might not be compatible with any new ideas the programmer might want to implement. This could become a stumbling block.
As a amateur programmer myself, here's the things I would try to implement in an upgrade:
1. Improved interface. This would include a better layout all-around. Everything from the episode creation screens to the information pages would all make use of tables and new HTML formatting methods. Most important would be to build a set of "default" formatting pages (XML) that would describe the general layout of the addventure, and which would be easily editable to make changes or improvements to the look and feel of the Addventure by editing only a few files.
3. Database implementation. I'd try to get some kind of online database up and working. The way I understand it now, many parts of the Addventure are a collection of HTML pages and large, rather unweildy text files. I'd try to put all the episodes into a database in order to save space and help organize the information better. This opens up possibilities for improved search functions and editing capabilities for moderators. Episode pages would be created on-the-fly as users requested them. As well, this opens up a wealth of easily calculated statistics pages. Basically everything that Adama currently does (statistics-wise) could be easily calculated and sorted by the OS.
3. Moderator capapilities. Moderators would be able to edit or delete information. A seperate interface would be created for them to work with the database (similar to the episode creation page except with a few more options).
4. Improved branching algorithms. Right now, the Addventure allows the user to input the number of branches and and then creates those episode numbers and readies them for creation. I'd like to see a new system where a certain number of episodes are fixed for addition (6 required), where an author may suggest a plot to continue, or can create his own. Of all the features, this would be the most difficult to "upgrade" from an existing addventure, as it might call for an entirely different type of "numbering" system.