I agree, though I always thought some stuff in Fourth Stage was a little unbelievable, like Takumi losing to Tomo (the professional driver from the Toudou school) because a gopher or something ran across the street, or him losing to God-Hand, the clearly superior driver, because he threw up. It makes sense, but it's not too possible. No driver would intentionally drag a race like that out to eight rounds, plus their tires would've had the wires coming out by then.
There has to be. I don't read the manga, but I hear reports of what happens on various websites. I think one of the first races in what is to become Fifth Stage is Project D versus a Miata and an Evo VII. Obviously there is more focus on Takumi's battle, which is said to be interesting because the Miata driver is actually better at braking than Takumi (remember that anyone who can out-brake Takumi can beat him, which is what he says when he raced against his dad in the Subaru). Someone watching the battle says that aerodynamics plays a huge role, which is true. The Miata driver at some point feels that he's dominating, so he pushes his rearview mirror away so he doesn't see what's in it. At the same time, Takumi turns his headlights off not to do the blind attack (since it wouldn't work anyway since his opponent can't see his mirror anymore), but because he figured that with his headlights down, it might make him just marginally faster since the pop-up design makes it a little less aerodynamic. He does get slightly quicker, then he tries to take the inside. Since the Miata driver wasn't really looking behind him, he gets surprised when Takumi is taking the inside, so his line changes and he goes a little outside, but his wing hits the wall and breaks off, which is key because FR cars like the Miata with such good weight balance tend to oversteer (which is something that Ryosuke mentions during the race), and the Miata eventually spins out and loses since it doesn't have as much downforce over the rear end to prevent oversteer.
Supposedly, there are two guys watching who jump in an NSX and drive away (possibly a future opponent), but the exciting part is that you see a guy in a Supra and Kai Kogashiwa (from Third Stage) in a new Toyota MR-S, who they are racing against at this very moment in the manga.