Your Dynamesh resolution is based on the size of your object. Try appending one of ZBrush's primitives to your subtools and see how the size of your model compares (Dynamesh 128 on a Cube3d is about 100K points). Chances are if you are getting really low point counts after dynameshing, your model's scale is too small.
An alternative to vanilla Dynamesh. You can set specific poly limits instead of resolution. http://www.zbrushcentral.com/showthread.php?177194-DynaMesh-Master!-unofficial-Information-Installation Not exactly the answer to your question, but hope it helps nevertheless.
Hi, Can somebody point me to a doc/wiki/forum where the dynamesh's resolution is explained? I'm having hard time understanding why resolution of f.e. 128 can give totally different mesh densities on two different objects of similar size. Does the fact of heavy down scaling the object before dynameshing it matter? AQ