Garages are still shit in GTA, but repo is improved. Most cars that I modify and then lose are successfully repo'ed. It's better than PS3, but still not great. With cars you obtain through missions, like the Stock Cars, those can all spawn in your player's fancy garage (the ones you buy for $40,000), and you can crash them/destory them and they will spawn again. However, if you purchase a car like one of the $1million sports cars, and then you're driving it high speed and accidentally destroy it while taking a jump, that car is gone as well as your $1million. It's complete shit.
It's even more confusing with aircraft and special vehicles like tanks. If you buy an aircraft, you can crash it and still have it spawn in your hanger. But, if you steal an aircraft and park it in your hanger, if you then crash that aircraft, it's gone. If you buy a tank and destroy it, then it will respawn in your hanger. But, steal a tank, park it, and destroy it, it's gone.
The system sucks and discourages sandbox play, which is really too bad.
I don't even get how Rockstar benefits from the current system in SP mode. I get in GTA:O, they want people to have to buy cars by playing the game or buying cash cards, but in single player GTA, I don't get why the game is so restrictive to keeping your cars and why you can't just tool around in whatever car you want if you happen to steal it. Saint's Row #1 had a better car system than GTAV does, released some 8 years later. Hell, I think GTAV's car ownership is worse than GTA:SA because at leas tyou could own as many cars as you had garages in GTA:SA. If you ditched/destroyed your car, the game charged you a nominal "tow truck" fee to restore it... It made me not worried at all to take out my best car to do a mission or to just tool around.