The last wall maps I generated of Ashgabat and Turkmenistan took a different turn, due to the heavy data requirements involved in a road atlas of the whole country. I was forced to learn Osmosis and the rudiments of Inkscape to edit SVG files first in order to reduce the volume of data and second to take the Maperitive-generated map and tweak it more easily. The lessons learned are now posted on the OSM wiki here. Comments on this tutorial are welcome.

Working with SVG images has its pros and cons, but on balance I think the map quality is better with this approach. That said, one can only wish that Inkscape and Osmosis were a bit more intuitive!