Who can help with the difference of 車をぶつけられる & 車にぶつけられる?
In my own understanding, the former means somebody else's car ran into the narrator’s car but the latter means the narrator was hit by a car. I'm not sure if I understand it rightly.
On "車をぶつけられる ", this time normally "your" car has damage in it by the collision when you don't control the car yourself. In other words, you are not directly involved in the collision, say indirect collision to you, so you might be mentally affected but not physically.
On "車にぶつけられる", this time normally "you" are directly hit by a car. You have the direct collision between you and car body. It could be used for the collision between your belongings and car if you are asked what objects hit your belonging.
Your understanding is partially fine, that is 車をぶつけられる and 車にぶつけられる are same meaning, but they make differences on the context. So, we need to compensate some words to distinguish them.
One of the meaning of (私は)車をぶつけられた is, as you say, somebody else's car ran into the narrator. However, we can also see 車をぶつけられる as follows:
(私の家に)車をぶつけられた。 / A car hit my house by someone.
(友人によって)車をぶつけられた。 / My friend drove my car and hit something.
(私は)車にぶつけられた normally means the narrator was hit by a car, but this also has other meanings.
(私の)車にぶつけられた。 / Something hits my car.
(私は)車にぶつけられた。/ I was pushed and bumped into the car(not a car accident).
車にぶつかった。Bumped into a car.
車をぶつけた。Hit the car (into something/someone else). The object of ぶつける is the thing that hits something, and に marks location of impact. It's weird for English speakers, I know. E.g.やくざの男が俺をその木にぶつけた。I think of this as being a causative verb, even though it's not, strictly speaking.
車にぶつけられた。Hit the car (as location. I was made to hit/run into the car by someone/something). そのやくざの男に木にぶつけられた。
車がぶつかった。A car hit (something, maybe me?).