Just a quick post about my testing with dwarves, echoing sythion they have help leveling quite a bit when conversion points come along early which gets me to bosses in non-vicious dungeons with extra resources. Only orcs tend to allow as much catapulting. However unlike orcs they don't have as much late game value which seems to be the bulk of the complaints. Also like I said they are good only after a few conversions usually and that is not always feasible. Either stacking bonus like orcs, or reduced cost would improve.
As a side note to make straight DR more interesting for vicious dungeons, maybe it can come with the added bonus of percent chance of ignoring a status effect. 3% per point or something.