The Asurans can't even kill Weir with the nanobots. As far as I'm concerned it's because the ancients never finished them or they were a failure in this sense. Until i actually see them kill a Wraith with nanobots I'm not buying it. And if I do I'm going to ***** to high heaven about how stupid it is given that they couldn't kill Weir, who as you may have noticed, hasn't spontaniously regenerated many otherwise fatal gunshot wounds lately.
All attacking nanobots would do would be damage cells, likely 1 or a few at a time. We already know that Wraith cells can multiply/regenerate so fast that they can seal up macroscopic holes in seconds. Attacking them with nanomachines would probably represent the single stupidest most ineffectual way you could ever possibly go about attacking them.