It has taken me three full months to review all my old GPS traces from the last years, and improve OSM data from them. In this time amount of data and its quality in the places where I have personal GPS traces and local knowledge of has improved a lot, for example, a big part of Madrid side of "Sierra de Guadarrama" is now in quite a good shape, there are few tracks/paths missing, and the ones that are already mapped are very precise (thank to GPS traces and legally useable aerial imaginery available in Spain).
There are lots of things left to do, though. Once you go outside of big cities data quality has to be improved (a lot), and even places with high population densities and aerial imaginery available are missing some basic road, features or lack adequate precision (coarsely drawn roads, roads shifted some meters away, data imports in the desperate need of manual improvents, rivers that go uphill and off course, etc.).
So it's now time to try and gather more people, and make them join the project. I know it's going to be very hard to do so, but will try some easy approaches to it. First, the "target market" is clear, people in the roadbike and mountain bike worlds. Specially for the MTB guys, GPS devices and personal trainers including GPS receivers are commonplace now, and the amount of GPS traces that get recorded every week is very important...but most of them end up on the user's local hard drive, erased, or at most, uploaded to Wikiloc or the like, where little use can be made of them. But people need some incentive to make an extra effort and deal with the tracks to, at least, upload them raw to OSM.
So the approach to get more and better data added to OSM from people in the MTB world is clear. Introduce OSM to them and show that current GPS maps (mostly Garmin ones) are already good enough for most purposes. Make them realize that improving these maps is orders of magnitude easier that editing raw Garmin maps (.imp, .mp, mkgmap, and all others), and the hard work is automated, and your edits can show in the downloadable .img maps in one day to one week time, depending on the map origin itself.
For most people, taking the time to open an OSM account, learn how to use Potlatch or JOSM, or even uploading raw GPS traces to the server is going to be more than they are willing to do, so for those people, or at least during the learning period, I'll try to proxy newcomers' request or data uploads myself, and to the (nasty) work of "drawing" the missing tracks / paths, from the GPS logs and the available imaginery.
I think this is worth trying, even though the availability of very good quality (lets call them) "non-official versions of commercial Garmin maps" for Spain that are widespread can make difficult to enroll people on the project, as they can see the effort as worthless, provided they already have the non-official high quality maps.
Well keep you posted :-)