@dankcushions Holy crap! I just figured it out.
In lr-mame2016, I turned on this setting:
Screen Shot 2021-02-25 at 3.44.20 PM.png
"Alternate Render Setting = ON" and look at the results:
And then in mame-2003-plus I found this setting:
Screen Shot 2021-02-25 at 3.48.58 PM.png
"Artwork Resolution Multiplier" and I set it to 2. Here's the results:
Now I just need to go through these games and see if there are any knock-on effects to these settings.
Hopefully this may help someone else who is in the same situation!