Those files have transparency by the looks of them. Try exporting as a PDF/X-4 file.
Thank you for your quick response. I've tried the following based on your recommendation:
- Exporting using the preset "PDF/X-4:2008"
- Exporting using my existing preset, selecting "PDF/X-4:2010" under the 'Standard' options menu.
In both cases the exported PDF returns the same low-quality background. Via a search through Google I also discovered recommendations for a similar issue dating back to 2012 where users recommended setting the opacity of the offending EPS file to 99.9% in order to force InDesign to render the transparency properly. Unfortunately this recommendation also solicited no change.
You might have better luck if you re-save those .eps files as native .ai
This solved the issue! It's obnoxious when I think of how often I'll likely have to re-save assets in this fashion, but it's better than accidentally printing something in that awful, awful quality. Thank you for taking the time to respond.
One factor might have an influence: Raster Effect Resolution in AI files, set them high enough, so that even upscaling them would give you enough resolution and never use EPS anymore as this is a file type from the past millennium and is not used anymore.