Do you race?
... Seriously people, you say one thing and then contradict yourselves with another. Some - like Famine's - are excellent, but who seriously wants to have a 20km nightmare through London or Chicago (or Area 51, as I saw in another thread of this nature, for that matter) when most of it consists of corners you hate?
And on that note, the only real cities that would be considered for a street course are the major ones - either capital cities or ones that EVERYONE knows. Places like Memphis might be big, but are they recognisable to the average gamer (and we're thinking in Japan and Europe as well as the States)? Yes? How about a track through Tampere then? Or Bilbao? (Bonus points to anyone who knows where they are ...)
Ahhhh. I get where you're coming from. Personally, I love 90° corners. The more ° a corner has, the more fun it is for me. Straights are for pure speed, corners are for feelin' lateral Gs

Off-camber corners are fun as are corners that change elevation. I also like corners you barely have to turn for, like shallow esses. I agree with you about the complaining that people do when it comes to 90° corners, I hear it on the forum too.
I can sympathise with you regarding the popularity of cities. I used to live in Danville, CA and I could design some pretty cool high speed courses through those streets, but who has heard of that city besides people who live in or around it?
John Madden (ex-football coach, now football announcer), Joe Morgan (ex-baseball player, now ESPN announcer) and Jerry Rice live(d) in a neighboring gated community called Blackhawk. Jerry has since moved from the S.F. Bay Area. Mark McGwire, when he played for the Oakland Athletics, lived in a town called Alamo. Jose Canseco, also with the Athletics, lived in San Ramon. Why do/did these players live in remote locations that few people have heard of? So they can be left alone. They get enough media attention before, during and after the games they play; they want to be left alone in their personal life.
A 20km street course? That would be around the same distance as four of the Grand Valley Speedway tracks strung together. I think that would be pretty cool, but I'm probably a minority on the forum when it comes to long tracks around and through a city. It seems to me that people like long courses when the course consists of many straights and a few corners. I like the inverse; wind me through corners and use short straights to connect them. I enjoy the layout through Chicago that Woolie Wool designed. It has enough of a mix that a lot of people could find it challenging and entertaining. I like it for the scenery aspect also.
The Area 51 track would be awesome and again, 'away from the norm.' but I seriously doubt Polyphony Digital could put it in the game because the United States' Government and what the area is used for. P.D. could only insert it if the satellite pictures were enough to scale everything from those models. The track would also have to carry a fictitious name. The fact that Area 51 has the world's longest runway is awesome. Did I mention I like hard braking? Talk about standing on the binders to make the first corner. Open up your beast along the longest runway and then feel the braking Gs as you haul your machine down from top speed to about 30MPH.