Lots of pretty maps based on OSM exist (even if the rendering at www.openstreetmap.org is pretty ugly). But routing, at least in my part of the world can certainly be improved.
It seems there are two major issues:
Address information is very sparse. If you are online and the routing engine is setup to use other sources of data it can be worked around. But for off line work, like OsmAnd where you are out of cellular coverage, this can be a deal breaker. In addition to collecting data by walking around, I have used the n76_oc_import user ID to import the public domain street address information for the county I live in.
Speed limit information is spotty. So even if you can locate the destination the best route may not be found and even if found the travel time estimates can be way off.
I render my own hiking maps, so a third area of interest is keeping the hiking trail data in my area up to date.