Restoration Puzzles sound like a Very Good Idea, actually.
Do what most MMOs do with longplay arcs: have a certain magic number of things that need to be fixed or accomplished, make it a pretty high number, and then anyone who wants to do so can contribute. When the magic number is reached, the players get shunted to a whole other server where everything has already been Restored, to start other work with the players who have already been on said restored server. Then new players can get shipped to the unrestored server.
Alternatively, you can put every new player on a clock, or pehaps even just a Restoration counter. The more things you restore, the closer you get to the Restoration, and get popped into a clean server and move on to new ages or areas of the cavern to work on. Like achieving the next level without the usual grinding involved. If you don't want to work in a certain area, go to another unrestored area and work in that. If you want to see and explore clean areas, do the restoration work.
This could be part of your characters 'level' setting, and each age they work to restore allows them access to the fully restored version afterwards.
I suppose ultimately this should be an optional career track feature, as some folks really won't want to go through this, and will only want to play completed areas. That's fine. They just won't get whatever bonuses come with having done the restoration track.
this also leaves open a career track for new Maintainer crews, who would have to go into whole new areas and map them out thoroughly, so restoration crews don't get killed.
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Lee Edward McIlmoyle
Adventure Game Devotee at large