Returned to Side By Side again, at least for a spell. I went and got #1 in the few remaining courses in arcade mode, to unlock the three bonus tracks, and then I got #1 in those to unlock the three bonus cars. Not a terribly difficult thing to do overall, took me less than two hours overall. The bonus tracks were a bit tough, since they're all point-to-point so there's no minimap to help you, just have to drive them until you memorize them enough to win.
One of the bonus courses is Akagi Downhill, btw. Pretty cool. I wonder if the other two are famous from Initial D as well?
The unlockable cars are mostly curiosities. There's Taito Van, Taito 1Box and Taito Truck. The truck one handles appropriately sluggishly, and the van is quite fast but doesn't turn very well. So not a real contender for Akina, but it would probably do well in the easier courses. I did manage to beat Bunta in Akina Downhill with it, though!
Speed is the magic that gives us direction