Gameplay: I think one key factor that the RR series really needs is online play on the console editions. It adds a lot of replay value, and it's an arcade racer...meaning that it's supposed to be ultra competitive. 8 racers online in this game would be insane.
Graphics:
Just import that models from the CG, mimic the lighting and there you go. Extra focus should be made on effects like the smoke and sparks. The smoke in next gen titles shouldn't look like transparent polys/sprites, and should look like actual volumetric smoke. If they can make it look like it's being spit from the tires, that would be awesome. The sparks should be very "arcade-like" in how they spit out but bounce realistically and should look smooth.
The cars should also have a really reflective look (just like in the shot ouromov posted). I really like the crazier designs as you go up classes.
Oh and I like the exaggerated trailing lights effect. At least have it as an option.
Tracks: I really like, as Mr Klaw mentioned, the "3D" aspect of Rage Racer's tracks. That in combination with crazy chicanes really makes for a thrilling roller coaster ride.
As mentioned, the locals need to seem alive and in motion, and I don't think it's too hard to do. I like the sensation of having a jet fly above your head as you are racing along, and helicopters passing by...just multiply that by 5 and there you go. Imagine seeing a hot air balloon right in front of you as you are going down a steep slope, or going behind a waterfall rather than beside it. They've been doing some of it, like the jet stuff...but just do more of it.
Music: the music has to trend towards Freeform. Yes, I'm biased, but I'd argue freeform and hardcore is the current day version of rave. With rave, anything goes, and the same definately holds true with freeform and nu-skool gabber. Plus, the previous RRs always evolved in the music...so I see no need to go back to an older style of music.
Hmm...well while typing this up I just realized that if Namco's not gonna read it it's gonna be a waste of time.
But I agree with a lot of the comments here.