For me multiple accounts to benefit paints or cars on your primary account is the same as glitching in other games.
People argue you can do it- so it must be ok. I see here in GTP it is apparently a widespread common practice.
I am old and therefore see things often in an old school way...I choose not to do it because I am sure the developers did not intend this kind of practice when making the game. I believe this is why they have modified the ability to do these things in the subsequent updates.
Would you have those things playing on a single account? No. Have developers tried to curb the ability to do this? Yes.
That is just my opinion- those who want to do it, do it. I won't.