More ways to rate Idea suggestions from other users
Instead of "I want this" for Idea suggestions, have a thumbs up and thumbs down option or duplicate idea or already implemented. Going through these ideas, I have skipped a lot of the idea sets as they are either in place, duplicates of others i have seen or not great ideas (or ideas that don't make sense). Once an idea gets lots of thumbs downs and minimal thumbs up, After your staff reviews (once it hits x number of thumbs down) and agree it's not such a great idea then the idea can get archived/deleted or something.
If you notice a trend of multiple people reporting that it's already implemented or duplicated, then after your staff
Or alternatively a comment box, for users to comment "already done, duplicate, etc", although you don't have much control on what people may include.
This will significantly reduce the number of suggestions that are posted/duplicated and help you focus on what most users want.