Agreed on 10 ft and 2d4 rounds sickened.
Tumble for the skill ranks, to help them get around opponents when above ground? Maybe Ability Focus (spores) for the feat?
A couple of corrections/additions:
1) Shouldn't the spore and dirtwraith flesh poison DCs be the same?
2) We need to explain how often the dirtwraith can use the spores and how big of a cloud it is. The original monster specifies 1/day, at least. Revising...
Spores (Ex): Once per day, a dirtwraith can release a 30 ft? radius cloud of poisonous spores centered on itself as a standard action. If the dirtwraith is currently animating a plant, this process requires a full minute during which the animated plant can take no other actions; the cloud is centered on the plant. As a result, dirtwraiths do not use their spore attack while animating a plant unless all their opponents are dead.
dirtwraith spores - Inhalation, Fortitude DC 12, initial damage 1d2 Con and is sickened for X rounds, secondary damage 1d2 Con. The save DC is Constitution-based. Corpses exposed to dirtwraith spores become grow a single new dirtwraith over a 48 hour period.
I went ahead and added the reproductive bit.