How about we create a new status, Archived.
A moderator could Archive a question. This would allow rep from the question to still be counted, and a special search 'isarchived' could be used to find it, but it wouldn't come up in normal searches, and would be marked so that Google wouldn't use them for search results.
This way old questions that aren't currently relevant, but were good for their time and have historical interest and maybe good discussion could be looked at by those who are interested, but those who just want to search for current stuff won't be bothered by them.
Note: This is for Meta sites only, and maybe for those huge subjective monster questions on SO.