I use a custom browser keyword search to find existing archived pages before saving one, personally. Eg: ar <URL> for:

  https://wayback.archive.org/web/*/%S

I'd imagine it would be useful for IA to implement some message for scenarios where a page has already been saved within a certain timespan and provide both a link to the already saved version and offer to save again. As this would mitigate mass savings of an identical page that can occur when some popular link is accidentally shared with the /save/ URL instead of the static URL or when it's a popular page that people want to archive.

Archive.is displays such a message (to the effect of, 'this page was archived <date>, if it looks outdated click save') and also redirects to the most recent copy.