Hey there,
With Playback Statistics, you can already use keyboard shortcuts or toolbar buttons to apply a rating as 1-5 or +1/-1. The menu is already built-in to the component, and you can make shortcuts or buttons out of any menu command.
To make a second rating though you would want Masstagger anyway as jazzthieve said, and use it to make a custom tag in your files - say %quality% or the like. You can use 'Set Value' to set a 1-5, or 'Format Value From Other Fields' for a +1/-1, for example -
Field name: QUALITY
Formatting pattern: $if(%quality%,$min(5,$add(%quality%,1)),3)
Script name: Quality +1
Field name: QUALITY
Formatting pattern: $if(%quality%,$max(1,$sub(%quality%,1)),2)
Script name: Quality -1
In Masstagger type a name for each script and save. Then in Preferences > Keyboard Shortcuts find the script under [context / playlist] > Tagging > Scripts. Or right-click toolbar buttons > Customize the same.
Then make another column for your playlist for %quality% like the one you have.
Cheers