Hello! I until quite recently lived and mapped in Los Angeles. I’ve definitely seen your name pop up on features and edit histories, had no idea you were from a different part of the world! In fact, I always wondered if your username was somehow related to Culver City.
First off, thanks for contributing to the region! I think every little bit helps, especially in a region as vast as Southern California. I will say as a local that I used multiple mapping softwares, including OSM-based and Google, to get around. OSM’s coverage of things like speed limits were often sparse, or perhaps worse, outdated as roads are reconfigured, so I think keeping things updated is really helpful for increasing parity with commercial apps.
To respond to your questions, I tended to find the biggest drawback of using OSM-based maps for car navigation was its lack of real-time traffic support (at least for the apps I’m familiar with like OSMAnd). Los Angeles has severe and fairly variable traffic, in which the fastest route can vary significantly hour-by-hour and taking the wrong one can lead to tremendous delay. Much of the reason I used navigation apps was to figure out if, e.g. I should get on the freeway or take surface streets at a particular time, even though without traffic one would obviously be faster. Even with correct speed limits mapped, if the router says it’ll take 20 minutes to get from Santa Monica to Downtown LA at 5:30pm it’s not particularly useful, and I wasn’t aware of an OSM app that could do that (though I could be wrong!).
I’ll add though that despite the “nobody walks in LA” refrain (and sorry for your unpleasant encounter!), I also worked to add a lot of the attributes you mentioned, like speed limits and stop signs, for the benefit of pedestrians. If you do dare to walk in Los Angeles, as I often did, it’s really helpful to know e.g. whether there’s a 4-way or a two-way stop at an intersection, or whether this road that has no sidewalks has a speed limit of 25 mph and two lanes or 40 mph and six lanes. Related to this, I tried hard to mark when there were or weren’t sidewalks along major roads and where there might be places to cross the street: this might be something you can do remotely while you investigate the other attributes if you’re so inclined.
But this info is useful for car routers too, especially to have all the info for someone to make a better one. For instance, I always felt that Google insufficiently penalized left turns across major arterials from minor side streets which don’t have the right-of-way: as in, it would often suggest them, when at rush hour such a maneuver is nearly impossible. If there were good coverage of stop signs, you could make a router yourself that adequately penalized such a behavior. Now if only we could map the presence of a left-turn signal…