Hardly OP. It's too fragile. Decent soviets can use AT guns and mines to 1 shot SC to death. When it reaches vet 2 it becomes good.
So it needs a big manpower price increase and slight health buff.
By the time the enemy rolls out an AT gun, the Scout Car will have already inflicted a lot of damage, perhaps enough to get to Vet 2 (which isn't that hard if you ask me). If the enemy rushed the AT gun, planning ahead for a Scout Car, he will have to make sacrifices in early game map control.
Mines can handle Scout Cars with ease, but I wouldn't want to rely on those alone to deal with it, since luck is a bit of a factor here, especially on bigger maps.
Once again, they're not OP'd, just hard to handle and a bit too cheap for the damage they are able to inflict. They come out very early and have the ability to dominate early game! Just read the post I made here yesterday, about the 3vs3 which was decided by a Scout Car on my part. Rolled it out, upgraded it and ran into 2 Soviet Scout Cars, making mine achieve vet 2 in seconds, allowing me to drive around behind enemy lines, killing enemy infantry by the bunch. We were already pushing towards their base without a single T3 unit on the field... Sure it was a stroke of luck to run into those Soviet Scout Cars, but still. I play mainly Ostheer, but I must say, it needs an increased price in order to balance things out.
Like I said before, in order to deal with it properly, Soviet has to adapt his early game, making Special Rifle Command a tricky choice as starter building...