Now this isn’t too important, and perhaps many would prefer not to have the extra worry - but I do feel like it would be a nice touch. Adding filth to vehicles on top of Fuel and Condition. Putting car washes around town for us to use - or adding them to the mechanic’s garage as an option.
Here’s a clean car vs dirty car. Not my best photoshop work but it is an Okay enough mockup.
Dirty car can have a negative effect on happiness. While a freshly cleaned car can have a positive boost!