I am concerned along teh same lines as you in regards to server load...
A Random Button, that just loads a random older post
An "I;m Feeling Lucky" attached to search
These are relatively easy
A full end customized search page with a lot of filter options and command entries to the search box.
Coding would be fun, but not only the load factor on the server, but also the system "Fart" factor if there is no search Limiter.
ie. Something that will return either the least active, or most active posts.
No limitations on the search (In a custom search) may also take time to return values (again; the load factor)
Gothi[c] is right in program timing (Rome, a day, and all that)
So maybe an "I'm Feeling lucky " button for search Parameters, and a "Random Thread" Button to start (???)