Au contraire Mon Ami ... Extensis Portfolio does not suffer from such shortcomings.
Here are screen shots of two EPS files I intentionally saved as EPS without a preview and then added to a Portfolio database. The first screen shows the thumbnail view and the second screen shows the detail view when the thumbnail is double clicked. The third screen shows a catalog I made some time ago with AI files without previews.
Of additional interest, the version of Portfolio that I am using is version 4 which is 10 years old. It will thumbnail and process the full size into a viewable JPG which can also be keyworded for searching later.