Functional cars are problematic due to a lack of open world and given the odd routes taken by Sims on bikes I doubt they'd stick to the roads! But there are a lot of cars and vehicles in debug. Including car wrecks and tires.
bb.showhiddenobjects and bb.showliveeditobjects (testing cheats is not required).
On console I find they don't all show up unless I do a blank search by opening up the search box and hitting enter without adding any search terms. I hear it's easier on PC. I just have to scroll a lot to find them. There are wagons and trucks too.
I thought we might get car maintenance with the Restoration Workshop kit but the items from that kit paired with some car wrecks and cars, etc could still make a cool garage. I've added something like this to a Sim's home and I've been working on another one too.
We definitely could use more garage doors, currently I use the ones from City Living. There's plenty of graffiti with Lovestruck, Get Together, Business and Hobbies and I think there is some in other packs but unsure when I'm not in my game. I use it quite a lot.