I like a lot of your ideas. When I wrote down some ideas that I had for cars myself I tried to make cars worthwhile and also implement why cars are used in real life and the changes that we are seeing when it comes to fuel economy.
Travel time is an interesting idea, I think it would need to be pretty generous with the travel time added as the game keeps inviting sims to festivals in completely different worlds, maybe just add 30 minutes (seconds) or something if you want to travel anywhere in the world.
Otherwise I thought that cars could give buffs or fill needs when traveling, fill the fun or food meter for example to symbolize that the sim have time to buy something to eat, or listen to music or the radio while in the car, or maybe it's just fun to drive the car just like sims have fun riding on bicycles. If you buy a car with more seats (like an suv) all the sims traveling in the same car will get the positive buffs. This makes cars appealing to families who want to travel together or elders who have difficulties filling needs. Different car models like sports cars will give goal-oriented sims something to strive towards like the celebrities in Del Sol Valley. There could be car related jobs (rabbit holes) where you could have trucks for delivery jobs or maybe a pickup truck for farm work or logging, maybe a fire truck or a police car.
I don't think EA/Maxis can edit existing lots so driveways would probably have to be a build/buy item. The car leaving the lot could still be animated and maybe it fades away after driving away so we don't have to worry about having actual roads connected to the lot.
Another thing that I think could be interesting is to add fuel economy to the cars as well. Petrol is expensive but can be refilled anytime, diesel is a bit cheaper but can only be used with certain car models, hybrid allows you to save up on fuel, electric needs to be charged, either at home (which will increase your electrical bills) or at a charging station (rabbit hole). The different fuel options could have different environmental effects as well if you have eco lifestyle.