An idea could be a showroom/garage storage where you can see all the cars you have in stock. This would just be a fun feature where you can get a more feel for what a storage for 100+ cars or whatever you have in stock looks like. A visual representation of your inventory. Instead of just a number.
So a separate facility which you can open up and see all your different cars in stock lined up.
Not a really super needed feature, but a nice touch if you have nothing else to add in the future.
If you want it to be a game mechanic you could also use the showroom as a limit on how many cars you can have in stock at once. If you buy a larger storage you can store more cars, but also pay more rent.
If you reach your showroom limit you want to empty the storage and sell off your cars at a discount to make room for new models. Instead of sitting with infinite stock forever with no cost.
This is a real problem IRL. Just check these images:
