There are many great suggestions that get buried into obscurity very quickly. Myself and other generally sort by new posts, so suggestions really only stay around in my feed for their first few days. It may be worthwhile to use the general feedback on a post to determine when something should and shouldn't be closed. If a post is gaining a large sum of support, it should definitely remain up. Posts that seem to have gone under appreciated or that most people missed also deserve a bit more time in the sun for people to try and find that suggestion. I'd only archive suggestions that get majorly no support, as those suggestions likely won't be getting put under evaluation.