The latest version of CSV Import does support a pseudo update. If you add an Entry ID column to your CSV file and populate it with the Entry ID in Connections the data will be updated rather than duplicated.
I say pseudo update because data such as addresses, phone, email and such are deleted and re-imported. Info like the name, bio, notes and visibility are updated. Additionally the category associations and images retain their links to the entry.
So, from what you said, it does sound like the current updating support will meet your needs.
I do not mention it as a feature because it has only limited testing but those that are using it seem fine with it and not have reported any bugs.
I hope that helps!