The ability to search SEDE queries was added recently, which is good, but this only searches on the title and description. Many of the existing queries don't really describe what the results represent in a way that's searchable.
I suggest adding a tagging system like the SE sites, so queries can be categorized and filtered to find things more easily, and also to see related sets of queries on the same topic (for example, browse all queries that find information about comments). Of course, this system doesn't need to go as far as SE sites with the likes of feeds and favourites, etc.
This would help alleviate the issue we have with duplicate queries -- if people can find existing queries more easily, they won't roll their own (or perhaps would clone an existing query and modify to suit, as opposed to writing one from scratch).
Yes, I'm aware that I may contribute to writing this; I'm just trying to gauge interest. At the very least, I volunteer to help do the initial tagging of the existing queries.