Edit: This post was made when the referenced tools were still considered experimental and not a part of the official builds. Now these tools and more are available from official builds.
There is a new option for adding fine detail but it is not fully in trunk yet. You would have to grab the GSOC Paint build from Graphicall.org.
Psy-f's build has curve and line tools that work as precision stroke brushes. Maybe that definition is not exactly correct but it's close enough I think. They work in sculpt mode as well but this requires extra geometry which is going to slow you down.
The idea here is to attach a 32 bit texture map(currently available) to your models UV's and then use that as a bump map. As is, this will not create real geometry but instead will create the illusion of extra detail which can be baked as a normal map. This seems to me to be the ideal situation for smaller detail since anyone would be hard pressed to tell the difference between real displacement and normal maps when it comes to the small scale that you are hoping to work with. This technique will also dramatically decrease your render times and the possibility of your computer locking up.
If, however, you insist on using true displacement then you can use this bump map in combination with the displacement modifier at a later stage. This will allow you to work with a lower poly model during the sculpt/modelling process and then you can crank up the multi-res detail in combination with a displacement modifier when it's time to render.
Even still, without the most excellent curve and line tools you can still paint bump maps but it's much harder to get the precision that these new brush tools provide.